Preheat temperature for Aluminum 6061-T6

By Lawrence (*****)

Date 09-10-2008 15:28

Welcome to the forum Tony

D1.2 (section 4.8) speaks to preheat

It indicates a maximum preheat and interpass temperatoure not to exceed 250 F for 5000 series or heat treatable alloys that contain more than 3% Magnesium.

6061 aluminum contains 0.8 to 1.2 percent magnesium so is not indicated in section 4.8

#1 Is your problem one of a low preheat that causes lack of fusion difficulties?

Or

#2 Is your problem one of excessive preheat causing difficulties in distortion, loss of strength post weld, or some other issue altogether.

Need more info

better responses will come with more data

By tonychen Date 09-11-2008 05:11

Hi, Lawrence

My question is low preheat that causes lack of fusion difficulties. But you explain section 4.8 " heat treatable alloys that contain more than

3% Magnesium". I realize we misunderstood D1.2 section 4.8. We suppose 6061-T6 should not be exceeded 250 F.This is wrong.

But I have two questions

1. "What's preheat temperature for aluminum 6061-T6?" Is there preheat temperature on other spec for Aluminum 6061-T6?

2.Why D1.2 section 4.8 has such limit temperature for alloys that contain more than 3% Magnesium? Is it easy to crack over 250 F?

Thank you!

By bozaktwo1 (***)

Date 09-12-2008 15:41

Not to make a splash in Lawrence's pond:

D1.2 contains some very strict tolerances concerning 6061-T6 heat input. I work with this material quite a bit, and have three pieces of advice:

1. Clean, clean, clean and when you think it's clean enough to weld, clean it again.

2. Weld hot and fast. I'm jamming through 3/16" tubes at 21v and 280 ipm wire speed with .045" and 100% argon.

3. I find that as long as I'm set up in accordance with my WPS, I can hold my preheat to 150 deg. F and still meet the heat input requirements.

The most important thing is to clean the metal. Good luck!

By Lawrence (*****)

Date 09-12-2008 17:51

Curt,

Thank you very much for splashing the pond :)

It made me go back to the code and do more research.

The index and table of contents are not so good for this particular question... The terms "Preheat" and "interpass temperature" do not lead to:
Table 4.5 Which expresses Maximum Heat Exposure at Temperature.

Table 4.5 gives some pretty strict tolerances for heat inputs just as you say!

I'm going to be doing some PQR's on aluminum this fall and winter so I appreciate anything that forces me to be a little better versed in D1.2

By 803056

Date 09-15-2008 01:05

In general, you do not want to preheat aluminum alloys. They are strengthened by heat treatment or by cold working. Both means of strengthening will be lost if the material is held at temperature for any length of time.

The tensile strength of 6061-T6 is on the order of 42 ksi in the as wrought condition. If you weld it successfully and in doing so, minimize the time at temperature, the weld is considered good if you can get it to pull at 24 ksi. In other words, even if you do everything right, the codes expect 6061 to lose about a 40% of its tensile strength.

I had the best results when I used heat sinks and blowers (fans)to minimize the time at temperature while welding and I never used preheat. If you are experiencing fusion type discontinuities, you need more heat input, i.e., Heat input = volts time amps divided by travel speed. Notice there is no place to factor in preheat temperature - don't!

The basics mentioned are applicable for both GTAW and GMAW.

Best regards - Al

By bozaktwo1 (***)

Date 09-15-2008 16:39

Oops. Yes, I meant interpass temp., not preheat.

As far as preheating Al goes, I wouldn't do more than enough to dehumidify the surface.

Lawrence, I recently had to perform some PQRs for 3/16" plate, single side V groove, no backing, CJP for GMAW in 2G/3G. I hope you don't have to try anything like that!