Porosity in titanium weld

Date 11-06-2007 19:07

We fabricate a lot of parts out of titanium and one of the parts we TIG weld is coming up with a considerable amount of porosity. One of the problems we have is that another company is leasing part of our building and they do a lot of aluminum grinding. A good amount of the dust ends up settling on some of our parts because currently there is not a wall to separate their operations from ours. The welders use alcohol or acetone to clean these titanium parts just prior to welding and they also clean the tooling they use. However, it doesn't take much for the aluminum dust to settle on a hot part they are welding.

My question pertains to how the porosity actually forms from the aluminum dust. I know that porosity forms from the freezing of gas released from the weld pool as it solidifies. It comes from the absorption of nitrogen, oxygen and hydrogen but what actually happens to this aluminum particle during welding that causes the porosity to form? Is there some sort of oxygen bubble that forms around the particle? Thanks.

By Lawrence (*****)

Date 11-06-2007 22:06 Edited 11-06-2007 22:08

Zeek

You shoud not be so quick to be convinced your porosity is caused by aluminum dust setteling on the work.

Having said that. Porosity in titanium GTAW is pretty rare and a sign of a gross process control problem.

Just because complete and in depth surface prep is written into your standard practices or even a specific procedure, it does not mean that it is occuring. You need to observe (personally eye wittness) the process that is producing the porosity from beginning to end. Because setteling dust is not going to cause a big problem unless it is mixed with atomized oils or chlorinated solvents that are not being removed prior to welding.

The dust setteling on a hot part will not cause porosity, it would have to rain down into the molten puddle in order to cause problems. It just seems hard to imagine that amount of aluminum dust in the air. If you do have that much dust, you better have resparators on everybody in the facility or you may have worse problems than porosity.

What titanium alloy and thickness are you welding ?

Groove welds? Fillet welds?

What gas shielding fixturing; Cups, backups, trailers, etc do you employ?

What is the surface color of the welds with porosity?

Is the porosity on the surface or discovered in RT and macro?

What code or standard practice guide do you comply to?

By Zeek

Date 11-06-2007 22:32

We manufacture components out of honeycomb panel. This particular joint is like welding 2 c-channel members together, although one member is made of 0.018 CP1 Titanium sheet and the other is 0.025" CP Ti plate.

This is a butt weld
Manually welded using Wp-9 torch and trailing shields. The trailing shields were made by the welders and have been working well for years. However, I am trying to make the switch to off the shelf trailing shields for better consistency.

The welds have been coming out silver with no discoloration within in the HAZ. The porosity is not on the surface and has been discovered once the part goes through x-ray. The porosity seems to be in the thicker member as well.

As far as specs, we have our own internal fusion welding spec that we use and the welders are certd per AMS-STD-1595A.

We have always had little areas of porosity with this particular joint in the past. Although, within the past couple of weeks, the porosity has been horrible. We had 3 different guys weld 3 different parts and they all had excessive amounts of porosity. It only seems to be on this particular part. I thought maybe they were using insufficient, or even excessive gas flow, but it seems odd that all 3 would be making the same mistake.