You slipped in there Kix,

Actually, 4043 does not heat treat and isnt rec if you are going to post weld heat treat. 

The exception is if you are welding less than o.75" material with a groove weld.  Apparently in this instance, the admixture pulls enough mag from the base metal to allow it to accept the pwht.  It does not hold true for a fillet weld in les than o.75" material. 

It also matters what you are tying to get to, the RT aging will only get to T4, the extra step gets to T6, which is what I need. 

Either way, you have to solution treat the material which is heating the piece 970-1000F for 65-75 min followed by a rapid quench--with no more than a 15 sec delay, that's quick!--in water that doesnt get to 100F during the process.

That's all I know

Rebekah 

When You finally find the rest of the heat treating info I would like to hear it too.

Hi rebekah
Yes it will have an adverse effect in my opinion.

The purpose of alloying elements.
Mg- is primarily responsible for high strength and higher hardness through the second phase Mg2Si in the heat treatable Al-Si alloys. Usually limited to 0.7percentMg as no further strengthening takes place beyond this concentration and even some softening of the alloy maybe incurred.

Si: dramatically improves fluidity and reduces the melting point. Alone it is not heat treatable but with Cu or Mg additions they respond favorably to solution heat treatment.

Therefore, if time and money was not a constraint it would have been better to remove all the welds with the wrong filler metal.
Filler 4643 will respond to the heat treatment due to the Mg2Si phase in the weld metal.
Filler 4043 will not respond to the heat treatment on its own as is a Al-Si alloy only.

So in your weld metal and fusion line area you will have areas that have responded to the heat treatment and other areas that have not. This will lead to fairly inconsistent mechanical properties.
Now on the other hand if you have substantial dilution with the base metal and the correct filler metal you can probably end up with something that might be acceptable depending on what your acceptance criteria is.
I don't know what the effect of the dilution of all the elements might have on the crack sensitivity ranges of Al-Si-Mg or Al-Mg alloys?

For the second part
If you have a bit of time and material just run a scenario of each of the quencing cooling you described.
weld a plate setup of what your application consists of. cut into sections. 1 macro 1 transverse tensile
do the heat treatment and quenching cooling and look at the macro and do the tensile. this will give you excellent real data.

I don't have any fo on the specific alloy you are welding, but I believe that the mechanics will work the same.

I have info on Al-Cu alloys but if I apply the same principles, my conclusion is this;

When you do a solution treatment you will create vacancies in the crystal lattice. These vacancies will serve as nucleation sites for precipitates< in this case Mg2Si, by lowering the nucleation energy required for precipitation. Now if you have a fast quench you will effectively trap these excess vacancies, which is advantageous as they then contribute to the formation of GP zones. (very fine metastable phases or precipitates) with annealing these metastable phases will then grow and become more stable. And in most cases this will cause them to become bigger and courser an more incoherent with the lattice which will improve your mechanical properties (aging) up until a certain point until the lattice incoherency is so big that it reduces the properties ( over aging).

If you do a slow quench or furness cool all your formed vacancies will diffuse out of the crystal latice and therefore leave less nucleation sites for precipitates, an will yield courser micro structure.

I conclude
fast quench from solution Temperature
24h age at room temperature to form GP zones
Aging at 120 odd Deg C ( or what you come up with) for 1h/inch

Good luck