Help! What Alu is my Impeller?

Save my weekend! I finally found an impeller but it needs a little help and Jack at MPD is booked up.
It's a Jacuzzi aluminum impeller and in a few hours I'm going to a buddy's shop to get a nick in the blade welded/ filled. Nick is about 1/8" X 1/2". Impeller is stamped PD 4100 MM.
Does anyone know what kind of Aluminium this is? My friend is a welding engineer so I'm sure he is competent but he is not a boater and is asking what alu.
Thanks in advance!

I'm a metallurgist, but not having the impeller in front of me for testing leaves me to an educated guess.
It's most likely Alloy 356.
SteveM.

Thanks Steve, I tried calling Jacuzzi but they have no clue. I cant get ahold of Jack at MPD but remember him saying something to the effect that there is a standard filler metal they use for the aluminum impellers. I just dont know what that is.
I want to make sure I dont make a repair that has to be redone later.

Most common casted aluminum is 356A.
Brian

Thanks Steve, I tried calling Jacuzzi but they have no clue. I cant get ahold of Jack at MPD but remember him saying something to the effect that there is a standard filler metal they use for the aluminum impellers. I just dont know what that is.
I want to make sure I dont make a repair that has to be redone later.
Try:
Scott Seastrom (Jack Seastrom is his dad).
They worked for Jacuzzi Brothers and for NAMJ before retiring and moving on.
Scott's Marine and Welding
(501) 624-0137
scottmarine@aol.com
111 Stonewall St.
Hot Springs National Park
AR 71913-4702
Good luck,

Thanks for your help guys. Got the impeller welded, shaped, and polished on Sat morning and back in that night. Woke up at 6 this morning to get every thing ready for the lake and boom, thunder and lightning.
Man I'm bummed. Guess Ill go change the Oil and grease my bowl.