Aluminum HAZ Strength 4043 vs 5356 1

[TJW]

I am hoping that someone can explain to me the strength values for heat affected zone presented in the Aluminum Design Manual Table A3.3 for 6061-T6. The ultimate tensile strength for 6061-T6 is 42ksi for non-HAZ and 24ksi for HAZ. That part makes sense. However, when looking at the yield strength, non-HAZ is 35ksi but the yield strength in the HAZ varies depending on the filler. Yield strength in HAZ is 11ksi if welded with 4043 and 15ksi if welded with 5356 (assuming for the moment t > .375). Why does the filler type affect the strength in the HAZ? The heat input seems to be relatively the same for the two filler types, so I can't figure out why the yield strength of the HAZ would vary due to filler.

Any insight would be very much appreciated.

Thanks,
Tom W

 

[kingnero]

Interesting question.
As you say, I do not think the filler should effect the HAZ, but I'm no metallurgist.

From a structural engineering point of view, here's my $0.02:
I am used to working according to eurocodes, there you will find HAZ reduction factors depending on:
-the base material (with differentiation between precipitation hardening and strain hardening alloys, and wrought and cast material)
-the thickness
-the welding process (GTAW or semi-automatic welding (= process 131 - MIG))

but the mechanical properties of the HAZ are nowhere linked to the used filler metal (the different filler metals are however tabulated, so they are considered for other aspects).

 

[gtaw]

The aluminum welding standards I have worked with specify the "as welded strength" regardless of the filler metal used. There is no mixing of the filler metal and base metal in the HAZ. The HAZ adjacent to the weld is base metal that has experienced temperature sufficiently high to undergo metallurgical changes. In the case of heat treatable aluminum alloys the HAZ can be overaged allowing alloying elements to precipitate along the grain boundaries thereby reducing the base metal strength. In the case of nonheat treatable aluminum alloys, the HAZ is most likely softened, again reducing the strength gained by strain hardening.

During tensile testing, aluminum alloys typically fail in the HAZ provided there are no defects in the weld.


Best regards - Al

 

[Ron]

Metallurgically, the 4043 is a softer material than 5356 and has a lower tensile strength. In the HAZ there is solutioning that occurs thus the strength of the 6061-T6 material is diluted by the temper reduction from welding as well as the lower strength of the 4043 filler material.

 

[dvd]

Here is an interesting article that I keep on file -

 

[Ron]

good article, dvd...thx

 

[TJW]

Thanks everyone for taking time to share your insights and thanks dvd for the article. I'll definitely keep that on file.

Tom