What grade of filler rod do I need to weld Aluminium car body?

Hello,
Thanks to all the contributors on this forum I can now DC tig weld aluminium.
Which brings me to my next problem - What grade of filler rod should I
be using?
The bodywork is for an Aston Martin - One book that I have describes it as Aluminium/Magnesium alloy of commercial grade half hard.
Another problem that I have had is hairline cracking - when I grind the weld level I sometimes get a short crack that is only just noticable; it runs along the joint. Is this poor preperation / technique or incorrect filler etc?
I have been using 5356 filler rods so far.
Thanks,
Simon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
not knowing the parent metal your dealing with I'd try 4064 filler it's less crack sensative than 5356 (more ductile of a weld) Dave

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks Dave,
I will try these, on a test peice to see how it works out.
I spoke to one of the Aston Martin specialists today. He said that they use pure aluminium filler rods. So I will also try those.
Would there be any dissadvantage in using pure aluminium?
Any comments and advice are most welcome.
Simon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
1100 is one of the suggestions I found in an old Kaiser Aluminum Sheet and Plate product information manual.
The book list two alloys as magnesium-type alloys that are easily formed. These are 5005 and 5050. 5005 is more easily formed while 5050 is stronger. It's quite likey that Aston-Martin used one of these.
The recommended filler for 5005 is 1100. The recommended filler for 5050 is 5183 or 5154. 5183 filler is the strongest while still being very ductile.
On the other hand, if you don't know anything about the alloy except that it is weldable, use 4043. There are only a few weldable alloys for which it isn't recommended.
Cheers,
Kelley

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry corection, meant to say 4043 (posting after midnight with drink in hand) Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

what did you end up using? helium? i have a Dc tig machine , and some aluminium welding work coming soon.
cheers, hubert
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It may be 3003 which is used on many cars and planes for the skin.
You can use either 5356 or 4043.
4043 is softer, more malleable, more shock resistant and has a lower melting point so it flows a bit better.
5356 is stronger, harder and more corrosion resistant.
--
Welding Instructor - South Seattle Comm. Coll.
- Divers Institute of Technology
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks Ernie and Kelley - I'm ready to give it another go now. Only problem is the welding shop is closed on Saturday and Monday is a holiday in the UK. So it will be Tuesday = more time to get the preparation right.
Another question I have is how much gas flow should I be using? I have a no7 ceramic (11.5 mm I think) and a 2.4mm 1%Lanthanated tungsten (only available 1% here still waiting for the 3.2mm to arrive)
Hubert Put "DC tig aluminium" into the search on this board. There is a good deal of knowledge. I followed the rules of thumb that Ernie has posted several times.
Simon
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.