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ALUMINUM Q&A BY TONY ANDERSON

Q: I am about to start welding procedurespecification development in preparationfor manufacturing a welded aluminumstructure. I have only developed weldingprocedures to the requirements of the

Amer ican Welding Society (AWS) D1.1 , Structural Welding Code Stee l, with which I am very familiar. Can you pleaseprovide me with any information on thedifferences I will need to consider when

working with the AWS D1.2, Structural Welding Code Aluminum ? Any informa-tion about areas that may cause me prob-lems during welding procedure develop-ment would be greatly appreciated.

A: You have asked a very good question.While the process of welding procedure

development for aluminum is in many ways the same as that for steel, there aresome very significant differences betweenthe requirements of the two codes. Also,there are some details associated with thequalification testing of aluminum thatmost certainly can cause problems if notfully understood.

Range of MaterialThickness

One fundamental difference betweenthese two codes, which is not normally a

problem, but which I will mention anyway,is that the AWS D1.1 steel code has a spe-cific limitation on thickness for which it isintended to be used. Steel less than 1 8 in.in thickness is not intended to be used withthis code but rather with the AWS D1.3,Structural Welding Code Sheet Steel . The

AWS D1.2 aluminum code has no suchrestriction.

Prequalification of WeldingProcedure Specifications

The AWS D1.1 steel code has, for many years, made use of prequalified weldingprocedures. The code provides the appli-cable requirements, which if conformedto, will allow the user to produce docu-mented welding procedure specifications

without the formal process of producing welding procedure qualification recordsand associated mechanical testing.

The AWS D1.2 aluminum code, on theother hand, does not have the provisionfor the prequalification of welding proce-dure specifications. All procedures devel-oped with the AWS D1.2 aluminum codemust be tested to be qualified in accor-dance with the code requirements. (Dis-cussion within the AWS D1G Subcommit-tee on Aluminum Structures would sug-gest that prequalified welding procedurespecifications may be something we seein the future.)

Guided Bend Testing

There are some significant differencesbetween the procedures used within thesecodes for guided bend testing. The partic-ular differences that I would like to point

Fig. 1 The mechanism for the wraparound bend test fixture, the preferred method for bend testing aluminum weldments.

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out are those related to the special bend-ing conditions that are required whenqualifying procedures in accordance withthe AWS D1.2 aluminum code. Becauseof the physical characteristics of some alu-minum alloys, there are some very specificdifferences between how some alloys arebend tested.

The M23 base alloys (6xxx series)may be bend tested under either of twoconditions, as-welded or annealed. In theas-welded condition, if the test sample isover 1 8 in. (3 mm), its thickness shall be re-duced to 1 8 in. (3 mm) thickness beforebending and then bent over a diameter of 21 16 in. (52 mm). Specimens of less than 1 8in. (3 mm) thickness shall be bent over adiameter of 16 1 2 thickness. Annealed spec-imens of M23 material of 3 8 in. (10 mm)thickness shall be bent over a 6 2 3 thicknessdiameter. The annealing practice that isconducted to the sample before bendingis as follows: Hold for 2 to 3 h at 775F(410C) then cool at 50F/h (28C/h) to

500F (260C). The rate of cooling below500F (260C) is unimportant. Welds made with M24 (2xxx series)

material shall be annealed and bent overan 8 thickness diameter.

Welds made with M27 (7xxx series)material shall be bend tested within two

weeks of welding. (This requirement is as-sociated with the 7005 materials abilityto substantially improve mechanical prop-erties through natural aging, precipitationhardening at room temperature.)

Welds made with F23 (4xxx series)filler metal on any M21, M22, or M23(1xxx, 3xxx, 5xxx, or 6xxx series) materialshall be bent in the same manner as M23material.

One other suggestion with regard tobend testing is to pay particular attentionto the note provided within the AWS D1.2aluminum code that states that the wrap-around guided bend fixture is the pre-ferred method of bend testing aluminum

weldments Fig. 1. Although the plungertype guided bend test fixture is an optionfor use within the code, I suggest that youuse the wraparound fixture, particularlyfor the higher-strength materials.

As can be seen above, the special bendtesting requirements for aluminum arerather extensive. I can assure you that if these requirements are not followed,there is a high probability that problems

will be encountered during procedurequalification testing.

Reduced Section

Tension Tests

One other item to consider is relatedto obtaining the minimum tensile strengthrequirements when conducting reducedsection tension tests. Minimum tensilestrength requirements for aluminum are

based on the annealed or overaged con-dition of the weld heat-affected zone(HAZ) dependent on whether welding thenonheat treatable or the heat-treatablealuminum alloys. Be aware that when

welding the heat-treatable aluminum al-loys, particularly the 6xxx series, careshould be exercised to prevent the over-heating of the base alloy during the weld-ing process. Careful adherence to inter-pass temperature should be maintained,and preheating limits should be observedto prevent excessive welding tempera-tures. Consideration should be given to

welding parameters, amps, volts, andtravel speeds that govern heat input dur-ing the welding process. These parame-ters may need to be adjusted in order tolower the overall heat input during weld-ing. The tensile strength of the HAZ of the heat-treatable alloys can be substan-tially lowered (to levels lower than thatacceptable to the code) if welded with ex-cessive heat input.

Conclusion

Yes, there are some differences be-tween the AWS D1.1 and AWS D1.2 codesin terms of welding procedure qualifica-tion requirements. These differences areto be expected as they address the proce-dure qualification of two substantially dif-

ferent materials. It has been my experi-ence that the two most common areas of difficulty experienced during the weldingprocedure development process for alu-minum are associated with bend testingand tension tests, which I have listedabove.

There are also other issues such asporosity and incomplete fusion, whichtend to be more prevalent in aluminumthan in steel. However, these are more re-lated to specific preweld preparationmethods and welding techniques, and notdirectly associated with differences incode requirements. o

TONY ANDERSON is corporate technicaltraining manager for ESAB North America.

He is a Fellow of the British Welding Institute(TWI), a Registered Chartered Engineer withthe British Engineering Council, and holds

numerous positions on AWS technical com- mittees. He is chairman of the Aluminum As- sociation Technical Advisory Committee for Welding and author of the book Welding

Aluminum Questions and Answers currently available from AWS. Questions may be sent to Anderson c/o Welding Journal, 550 NW LeJeune Rd., Miami, FL 33126, or via e-mail at tanderson@esab.com .