Aluminum Applications in the Rail Industry

8/12/2019 Aluminum Applications in the Rail Industry

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1LIGHT METAL AGE, OCTOBER 2007

Extrusion Research Challenges

Aluminum Applications in the Rail Industry


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2 LIGHT METAL AGE, OCTOBER 2007

Introduction

The connection between the aluminum industryand railroads goes back a long way, in fact almostto the inception of the aluminum industry itself in1888. The first reported use of aluminum in this

market was by the New York, New Haven, and HartfordRailroad in 1894 when it built a special lightweight car

with aluminum seat frames. This was followed in 1931by the development of the all-aluminum hopper carsfor freight.1At the Worlds Fair in Chicago in 1933 thefirst two main-line, all-aluminum, passenger railroad cars

were exhibited.2The development of further applicationsof aluminum in the railroad area continued especially

following World War II when excess material capacity wasavailable. Developments have continued apace, drivenby aluminums light weight, corrosion resistance, andoverall durability. This paper provides an update to thisinteresting and dynamic market, explores some recentadvances in the technology, and discusses the potentialimpact of newer aluminum alloys and fabricationtechnologies, such as Friction Stir Welding (FSW).

A Proven Material in Rail: Experience with aluminumover the past several decades has resulted in numerousapplications for the metal not only in freight cars, butalso in light rail and inner city commuter trains, metros,and underground trains as well as in the express, intercitypassenger trains. There is also considerable use ofaluminum in the advanced high speed trains such as the

Acela, the TGV, Transrapid, Shinkansen, and Pendolino-type trains, and the futuristic magnetic levitation (Maglev)trains.

Aluminum Applications and Advantages

Freight Applications: One of the most significantapplications of aluminum in rail has been in thedevelopment of freight cars for the transportation of arange of commodity materials, especially coal. Typically,rail cars are designed for a 30-year life, and materialsdevelopments have tended to evolve gradually.3However,much of the existing rail stock is now approaching theend of its original design life. This, together with therecent high demand for the transport of low-sulfur coal

from the western mines to the eastern markets, hascaused a boom in the construction of coal cars. An articlein American Metal Market (AMM)4forecast that deliveriesof railcars will approach some 60,000 units per year by2009 and projected a 50% growth in coal car deliveriesover the five years starting in 2005. In a more recentarticle, AMM5 estimated that some 27% of these cars

will be aluminum. The lighter aluminum railcar bodies,about two-thirds the weight of the comparable steel body,enable a greater payload. The higher payload capacityrepays the higher initial cost of aluminum in less thantwo years, and the resistance of aluminum to corrosionby the high-sulfur coal ensures long durability for thesecoal cars. In addition to the operational advantages, theU.S. DOE has reported that the conversion of coal carsto aluminum has facilitated a significant decrease inthe total CO

2emissions produced by the transportation

sector.6To further emphasize this application, FreightCarAmerica, a builder of rail cars, recently celebrated thedelivery of the 100,000th aluminum car in a ceremony

with its customer in December, 2006.7 Figure 1 showsa line of open-top, hopper cars for hauling coal madeusing aluminum plate and extrusions.

The use of aluminum in coal freight cars is only oneof many freight applications. Aluminum cars are used

to transport a variety of metal ores and minerals frommine to market. In all these applications the high specificstrength (strength to weight ratio) of aluminum enablesincreased payload and fuel savings. Johnstown Americas

website8offers an excellent overview of the large numberof designs available in aluminum freight cars. Recently,FreightCar America has been able to redesign its Bethgonline of cars to further increase capacity through use ofalloy 6061 extrusions. In other products, aluminum sheetside walls offer improved aerodynamics and lower windresistance and eliminate the need for paint, therebylowering operating costs.

Another recent and popular product has been theautomotive vehicle carrier. Here the car, enclosed withaluminum sheet, protects new vehicles in transit from

the factory to the dealer. Extensive use of aluminumextrusions has enabled lightweight designs, with highcarrying capacity for larger vans and SUVs, and especiallylarge doors to facilitate rapid loading and unloadingoperations. In Johnson Americas August 3, 2004press release on the delivery of their first productionaluminum vehicle carrier (AVC) as shown in Figure 2a,

Jack Thomas, president, First Union Rail was quoted assaying, We are pleased to be innovators in the vehicletransportation field by being the first to lease the new

AVC cars to Canadian National (CN). With theirprojected long service life and corrosion-free aluminumsuperstructure, we are confident the AVC cars will serveCN and its customers well. In addition, Bill Wiles, vicepresident, automotive for Johnstown America stated,Rugged, yet light, the AVC is designed for minimum out-of-service time, further reducing the cost of operation. A

Aluminum Applications in the Rail IndustryBy Michael Skillingberg, The Aluminum Association, Inc. and

John Green, JASG Consulting

Figure 1. Aluminum intensive open-top hopper cars. (Photos courtesyof Freight Car of America)

Reprinted with permission, 2007Light Metal Age
http://www.lightmetalage.com/http://www.lightmetalage.com/http://www.lightmetalage.com/


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longer-term benefit is that through an AAR exemption,the aluminum superstructure never needs recertificationover its extended life span.

One of the most significant advantages of aluminumis the application of internally-stiffened large hollowextrusions to fabricate moveable side walls for freightcars. As compared to conventional steel walls, this typeof design enables the wall to be fabricated with manyfewer parts, reducing the extent of welding required, andis significantly lighter, which has the further advantagethat the wall can be manipulated by a single worker,thereby saving labor. The 6xxx series alloys (aluminum-magnesium-silicon) normally used for this applicationoffer excellent extrudability, as well as moderate strengthand high corrosion resistance, and as a result the wall canbe used unpainted and the cut ends of extrusions neednot be sealed. The overall aluminum side wall is virtuallymaintenance free (Figure 2b).9

dominant. These rail cars are made of longitudinalextrusions that run the total length of the car, andthe individual extrusions are then welded togetherlongitudinally. In the case of the Washington, DC metrosystem, these extrusions are 75 feet long. The overallstructure is then stiffened by horizontal members that areattached around doors and windows. The floor structureis strengthened by the use of the hollow, integrallystiffened extrusions and the area near the wheel bogieis strengthened by several transverse members. This

design also minimizes the number of parts required,as compared to steel fabrication, and simplifies andreduces the amount of welding.9 The overall resultis a stiff structure that is able to handle complex loadsand aerodynamic forces that result from going throughtunnels, and which is about two-thirds of the weight of acomparable structure fabricated from steel.

This weight reduction is especially significant forcommuter trains with frequent stops as it enables energysavings in service and reasonable acceleration betweenstops (Figure 3). The other advantages of aluminumin durability and corrosion resistance also provide lowmaintenance costs and long system life.

Lastly, another advantage of aluminum freight cars is

that they retain a high salvage value when recycled atthe end of their life cycle. In a recent example, severalhundred 100-ton hopper cars initially built around1967 were recently sold for almost 90% of the originalmanufactured cost!

Commuter and Passenger Trains: The commuter andpassenger rail category has an enormous variety of traindesigns and structures. These range from the light rail,commuter and metro trains, and trams to the moresubstantial inter-city and express trains. Alstom, a leadingtransnational corporation and producer of the EuropeanTGV and of Pendolino-type trains, has a comprehensivedescription of some of these trains available on their

website.10

In these trains the structural loads imposed by thepassengers and their seating dictate the designs. Herethe advantage of long aluminum extrusions has become

The weight reduction enabled by the use of aluminumis also critical in the newer inter-city tilting, or Pendolino-type, trains. Pendolino, which means pendulum in Italian,

was the company that pioneered this tilting developmentand was taken over by Alstom in 2002. Just as a cyclistleans into the curve as he rounds a bend, the tilting

train leans into curves and can negotiate bends at ~35%higher speed than compared to conventional trains.This development is especially important in improvingthe speed of inter-city service without making significantand costly track modifications or building new rail linesexclusively for high speed service. The Acela train,

which operates in the northeast corridor of the U.S.,(Figure 4) is one example of the tilting train, though inthis case some design considerations compromised theextent of the benefit that could be derived by the tiltingmechanism.

Many tilting, Pendolino-type trains are operatingthroughout Europe (the French TGV), and one recentlyachieved the Czech Republic rail speed record of 237km/hr. Another recent development in some of thesetrains is the regeneration of electricity when braking.Operational experience indicates an energy savings of

Figure 2b. High capacity railcar with sliding aluminum sidewall. (Photo Alstom Transport)

Figure 2a. Aluminum Vehicle Carrier (AVC). (Photo courtesy of John-son America Corp.)

Figure 3. DC Metro train. (Photo courtesy of http://en.wikipedia.org/wiki/Washington%2C_D.C.)


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and corrosion performance,14, 16but the development offriction stir welding, which is discussed hereafter, maychange that situation.

It is interesting to note that the advanced trains are stillusing these similar materials. For example, the JapaneseShinkansen uses 5083 alloy, and also some 7075 material,

which is more frequently used as an aerospace material,while the German Transrapid uses 5005 sheet for panelsand 6061, 6063, and 6005 for extrusions.

Recent Alloy Developments: Some recent research forimproved rail materials has been evaluating neweraluminum alloys containing scandium additions.16

Scandium provides the highest amount of strengtheningper atom percent of any alloying element when addedto aluminum. Small additions (0.1-0.2 wt%) have beenshown to improve mechanical properties, refine themicrostructures of wrought aluminum alloys, and improve

weldability by reducing hot cracking in the weld region.

Since all of these factors are relevant to rail applicationsof aluminum, a study was conducted to establish whetherscandium-containing 5xxx, 6xxx, and 7xxx alloys couldbe used in conjunction with advanced welding technologysuch as friction stir welding, to improve the performanceof aluminum alloys for rail applications.14

While previous studies showed that scandiumadditions improved weldability of 6061 alloy, this studydemonstrated that scandium additions reduced thestrength of 6061 and did not refine the grain size. In thecase of the 5456 alloy, the addition of scandium did refinethe grain structure and improve mechanical properties;however, the intergranular corrosion performance wasadversely impacted.

In the case of the 7xxx alloy, however, scandium addi-tions did significantly improve mechanical properties,

weldability, and corrosion resistance. Because of higher

mechanical properties, however, the extrusion rate ofthis alloy is somewhat slower, and hence production costscan be expected to be higher. So the trade-off is whetherthe improvements in mechanical properties, weldability,and corrosion resistance from the scandium addition tothe 7xxx alloy are sufficient to overcome some increasein material cost. To date, scandium has only been used inrelatively small quantities in high performance sportinggoods such as baseball bats and archery arrows, and itremains to be established how widespread the use of

these alloys will become. As the construction techniquesof the advanced trains become more akin to aerospacetechnology, it could well be that the scandium modified7xxx alloy could provide some significant systemadvantage. For example, a higher strength extrusion(due to the addition of a scandium-containing alloy)

when used to build a total assembly might enable certaindesign improvements such as the need for less materialresulting in a lighter, more fuel efficient system.

Friction Stir Welding:As pointed out in the AluminumIndustry Technology Roadmap,17 the technologyof aluminum joining has advanced rapidly in recent

years. Developments in FSW especially have been mostsignificant and have provided aluminum with a significantcompetitive advantage in some markets (Figure 7). Since

its inception in the early 1990s, FSW has advanced mostrapidly with aluminum due to its combination of lowmelting point, high thermal conductivity, and ductilityand is now being used on the external tank of the SpaceShuttle and the Eclipse business jet. FSW has enabledthe joining of previously difficult to weld alloys, often

with improved mechanical properties and corrosionresistance. Experience with FSW in the fabrication of fastferries and bridge decks indicates that the process hasincreased automation, improved dimensional tolerances,reduced residual stresses, and lowered manpower needs.The process is especially advantageous in the fabricationof long butt welds, but welding along curves and aroundcylinders is now also possible.

Table I. Aluminum attributes in rail applications.

Figure 7. Schematic of Friction Stir Welding.

While FSW is being developed for other metals as well,its application for aluminum has been most dominant.One reason for this is that tooling costs are relatively lowfor aluminum. The relatively low melting temperatureof aluminum (~660C) as compared to steel (~1,500C)for example, ensures that the wear of the spinning tooland the forces required for the welding process are muchreduced.

For the fabrication of rail and passenger cars, FSWis an ideal process for the butt welding of the lengthylongitudinal extruded sections that comprise the roof

and floor sections of the cars. The fact that the technologyenables the joining of some alloys that traditionallyhave been difficult to weld, e.g. most 2xxx and 7xxx


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and corrosion performance,14, 16but the development offriction stir welding, which is discussed hereafter, maychange that situation.

It is interesting to note that the advanced trains are stillusing these similar materials. For example, the JapaneseShinkansen uses 5083 alloy, and also some 7075 material,

which is more frequently used as an aerospace material,while the German Transrapid uses 5005 sheet for panelsand 6061, 6063, and 6005 for extrusions.

Recent Alloy Developments: Some recent research forimproved rail materials has been evaluating neweraluminum alloys containing scandium additions.16

Scandium provides the highest amount of strengtheningper atom percent of any alloying element when addedto aluminum. Small additions (0.1-0.2 wt%) have beenshown to improve mechanical properties, refine themicrostructures of wrought aluminum alloys, and improve

weldability by reducing hot cracking in the weld region.

Since all of these factors are relevant to rail applicationsof aluminum, a study was conducted to establish whetherscandium-containing 5xxx, 6xxx, and 7xxx alloys couldbe used in conjunction with advanced welding technologysuch as friction stir welding, to improve the performanceof aluminum alloys for rail applications.14

While previous studies showed that scandiumadditions improved weldability of 6061 alloy, this studydemonstrated that scandium additions reduced thestrength of 6061 and did not refine the grain size. In thecase of the 5456 alloy, the addition of scandium did refinethe grain structure and improve mechanical properties;however, the intergranular corrosion performance wasadversely impacted.

In the case of the 7xxx alloy, however, scandium addi-tions did significantly improve mechanical properties,

weldability, and corrosion resistance. Because of higher

mechanical properties, however, the extrusion rate ofthis alloy is somewhat slower, and hence production costscan be expected to be higher. So the trade-off is whetherthe improvements in mechanical properties, weldability,and corrosion resistance from the scandium addition tothe 7xxx alloy are sufficient to overcome some increasein material cost. To date, scandium has only been used inrelatively small quantities in high performance sportinggoods such as baseball bats and archery arrows, and itremains to be established how widespread the use of

these alloys will become. As the construction techniquesof the advanced trains become more akin to aerospacetechnology, it could well be that the scandium modified7xxx alloy could provide some significant systemadvantage. For example, a higher strength extrusion(due to the addition of a scandium-containing alloy)

when used to build a total assembly might enable certaindesign improvements such as the need for less materialresulting in a lighter, more fuel efficient system.

Friction Stir Welding:As pointed out in the AluminumIndustry Technology Roadmap,17 the technologyof aluminum joining has advanced rapidly in recent

years. Developments in FSW especially have been mostsignificant and have provided aluminum with a significantcompetitive advantage in some markets (Figure 7). Since

its inception in the early 1990s, FSW has advanced mostrapidly with aluminum due to its combination of lowmelting point, high thermal conductivity, and ductilityand is now being used on the external tank of the SpaceShuttle and the Eclipse business jet. FSW has enabledthe joining of previously difficult to weld alloys, often

with improved mechanical properties and corrosionresistance. Experience with FSW in the fabrication of fastferries and bridge decks indicates that the process hasincreased automation, improved dimensional tolerances,reduced residual stresses, and lowered manpower needs.The process is especially advantageous in the fabricationof long butt welds, but welding along curves and aroundcylinders is now also possible.

Table I. Aluminum attributes in rail applications.

Figure 7. Schematic of Friction Stir Welding.

While FSW is being developed for other metals as well,its application for aluminum has been most dominant.One reason for this is that tooling costs are relatively lowfor aluminum. The relatively low melting temperatureof aluminum (~660C) as compared to steel (~1,500C)for example, ensures that the wear of the spinning tooland the forces required for the welding process are muchreduced.

For the fabrication of rail and passenger cars, FSWis an ideal process for the butt welding of the lengthylongitudinal extruded sections that comprise the roof

and floor sections of the cars. The fact that the technologyenables the joining of some alloys that traditionallyhave been difficult to weld, e.g. most 2xxx and 7xxx


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alloys, provides a further competitive advantage. As thefabrication techniques for the advanced trains becomelike those of the aerospace industry and if history there isany guide, the application of FSW to the rail industry willimprove the welding of rail cars, automate the process,and lower overall costs. A recent study at the SouthDakota School of Mines & Technology indicated thatcost savings of greater than 20% could be obtained withFSW as compared to the baseline bolted design whenfabricating aluminum hopper cars.18

The FutureStriving for Sustainable Mobility

In the U.S. the development of passenger rail serviceshas lagged behind the rapid growth of air traffic andair terminals and the continuing development of theinterstate road system. The status of the rail industry

was highlighted in a recent news article.19 The articlepointed out that high speed rail got attention in the1990s when the U.S. government designated high speedrail corridors around the nation. Now while there are 11designated rail corridors through 28 states, the articlenotes that actual development of high speed rail servicehas slowed to a crawl or become completely dormant. Allthis is because of a lack of both federal and state funding

for major infrastructure projects. The article goes on toquestion whether there is a real market for rail ridershipin this country. Further, it is noted that virtually all therailroad tracks in the U.S. are privately owned by freightcompanies that are running slower, heavier trains, andthese companies are not interested in mixing advanced,high-speed passenger trains with the slower movingfreight trains.

The U.S. situation is in marked contrast to that in manyother countries in Europe and Asia. In Germany, France,and Japan, for example, the rail industry is driven bysignificant government investments. The national highspeed train systems are viewed with a certain amount ofnational pride and prestige and as an aid to tourism, andthere is a continual interest in upgrading performance

and establishing speed records between cities.As in several other areas of commerce, much of thefuture of rail transportation will probably be impactedby the growth of rail infrastructure in China. China isalready investing heavily in a large array of infrastructureprojects. In advanced rail technology, the Chinese havesurprised many by jumping ahead to operate a highspeed Maglev system (established by the German makersof the Transrapid system) and also are importing largenumbers of different advanced trainsets from Europe toestablish a national infrastructure. Of course, it remainsto be seen how all these different national approaches

will work out in the development of effective nationaltransportation systems.

One major challenge for all countries in this new

century surely will be the development of transportationsystems that ensure sustainable mobility. With growingevidence of climate change and global warming, it will beincreasingly difficult for the nations of the world to ignorethese issues. Almost certainly, national transportationsystems will strive to become as energy efficient andenvironmentally acceptable as possible. People aroundthe world will also seek to travel more both for businessand recreation and so the concept of enabling thisincreased mobility in a sustainable manner will becomemore important.

While it is not clear how the various rail systemsdiscussed will evolve and which technology will becomepredominant, it is clear that the many attributes ofaluminum for the transportation industry, and especiallyfor rail cars and passenger trains, will undoubtedlyensure aluminums critical role in the development of

sustainable mobility. Aluminum is already consideredone of the most sustainable metals due to its excellentrecyclability and the fact that recycling saves ~95% ofboth the energy and emissions, as compared to makingthe metal from the ore.

The results from recent modeling of comprehensivelife cycle studies indicate that aluminum will becomeclimate neutral by the year 2020.20 To date, noother metal has been able to make such a claim. Inother words, the fuel savings achieved through the

lightweighting of transportation vehicles by increasedaluminum usage, and the resulting reduction of CO2

emissions, will more than compensate for the additionalCO

2 emissions generated by the production of the

additional metal. In rail transportation, the data has notbeen as well documented but in the case of automobiles,a 10% reduction of vehicle mass translates directly to afuel saving of 6-8%, with an equivalent reduction in theCO

2 emissions derived from the fuel. Accordingly, the

various attributes of aluminum and especially its lightweight, durability, and corrosion resistance will ensurethat aluminum sheet and extrusions will have a strongfuture in the development of rail transportation systemsaround the world, and in striving to attain a situation ofsustainable mobility for future generations.

Editors Note: For more information on how to obtain AluminumAssociation publications, go to: www.aluminum.org/bookstore.

References

1. Aluminum by Alcoa, p. 58, Alcoa, 1969.2. Langan, Timothy, High Strength, Lightweight Car

Bodies for High-Speed Rail Vehicles, final report forIDEA Project 32, November 2004 (www.ntis.gov).

3. Zehnder, J., Al in the Rail Transportation Market,Mat. Sci. Forum, Vols. 390-402, pp 3-8, 2002.

4. Burgert, Philip, American Metal Market, September27, 2004.

5. American Metal Market,July 24, 2006.

6. Mitigating Greenhouse Gas Emissions: VoluntaryReporting (Report DOE/EIA-0608 (96), U.S. Depart-ment of Energy, 1996).

7. http://www.freightcaramerica.com/investor/news/121306.htm

8. Johnstown America website: www.johnstownamerica.com/products/fcp_coal.htm

9. Altenpohl, Dietrich,Aluminum: Technology, Applicationsand Environment, 6thEdition,The Aluminum Associationand TMS, 1998, pp. 349-352.

10. Alstom website: www.transport.alstom.com11. Wikipedia: http://en.wikipedia.org/wiki/Pendolino12. http://www.gluckman.com/Maglev.html13. Aluminum by Alcoa, p. 60, Alcoa, 1969.14. Repair and Maintenance of Aluminum Railcars

Publication #65, The Aluminum Association, August1984.

15. Welding Aluminum Theory and Practice, TheAluminum Association, 2002.

16. Langan, Timothy, High Strength, Lightweight CarBodies for High-Speed Rail Vehicles, final report forIDEA Project 32, November 2004, pp. 22-23 (www.ntis.gov).

17. Aluminum Industry Technology Roadmap, TheAluminum Association, p. 36, February 2003.

18. Allen, Casey, et al., Friction Stir Welding of anAluminum Coal Hopper Railcar,Friction Stir Welding andProcessing IV,TMS, 2007.

19. USA Today,November 4, 2006, p. 4A.20. Overbey, R., Sustainability What More Should

Companies Do, presentation to Conference Board, June2005. http://www.greenbiz.com/news/news_third.cfm?-NewsID=28278

Aluminum Applications in the Rail Industry

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