Tig aluminium porosity

When trying to weld some unknown aluminium scrap pieces together, I found out that the joints I produce, although nice looking and with
sufficient penetration are porous internally and weak. Does this means my pieces are not clean enough or does this mean the filler is not the correct one for my base metal?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sounds like some of the aluminum you had was 2024. It does not like to weld.
It has to be very clean and free of oxides.
It also has to be a 1000, 3000, 5000 or 6000 series aluminum.
The only 2000 series aluminum that can be welded is 2219 (copperloy used in truck ramps)
The only 7000 series aluminum that you can weld is 7005 used in bike frames.
4000 series is only used for filler metals.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Maybe water near weld if no preheat and not enough cleaning. This is bigger problem with fast MIG welds than slow TIG welds that heats bigger area around weld.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I'm always impressed by the speed at which you answer, Ernie. Thanks a lot.
2000 are aluminium-copper alloys. Interestingly, I was able to make a non-porous weld by adding a lot of filler. I suppose that the base metal was then diluted enough to change its caracteristics.
For the enjoyment of the group, I should also post the following links I found searching for more info on aluminium metallurgy:
http://www.secowarwick.com/pressrel/articles/aluminummetallurgy.htm is a general explanation of the series and their uses.
http://www.aircraftmaterialsuk.com/data/aluminium/alalu.html has tables comparing various international designations and links to typical uses.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.