Your question is not simple to answer.

It is typical for most weldable aluminum alloys to become softer in the weld and heat affected zone.

Different alloys require different heat treatments to regain their original properties. Some cannot.

If you tell us the type of alloy and thickness your base metal (substrate) is and what your choice of filler wire is, some of the board posters may have some good advice for you.


Here are some links to common questions similar to yours;


Why is my aluminum weld much weaker than the parent material?
http://www.lincolnelectric.com/knowledge/articles/content/alumfaq.asp#question2

What is the proper stress relieving practice for aluminum welds?
http://www.lincolnelectric.com/knowledge/articles/content/alumfaq.asp#question6

What are non-Heat treatable aluminum alloys?
http://www.key-to-metals.com/Article22.htm

What filler do I use for 6061T6 ?
http://www.alcotec.com/qanda5.htm