aluminum mig welding

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I am a newbie with some aluminum welding questions.I recently purchased mm251 with 15A spoolgun. I have been practicing and every thing seems to be real close but I am concerned with the amount of black and dirty burn marks around the weld. I only have experience with tig welding aluminum and that process is spotless if done correctly.  I am using 100 %Argon, cleaning the aluminum with a dedicated ss brush, 5052 aluminum, 5356 .30 wire and I end up with a weld that looks clean but black for about 1 inch on either side and in front of the weld pool. I am using a 10-15 degree push angle.  I have talked to the place where I bought the welder and they said if the weld looks good don't worry about it. The person that gave me that advice looked like he was 16 years old so I am taking that advice with a grain of salt. My concern is that if you are pushing a weld bead into a black dirty mess that weld cannot be great. I am inexperienced in mig welding so any advice is good    Thanks Tungstenburner
Reply:You can expect a bit of smut along the sides.  Ensure you have cleaned the material.  You seem to have done that.  A bit more gas flow and keeping the nozzle as close as possible to the plate will also help.  Not sure about it but I think the black is mostly magnesium oxide.
Reply:If I'm at a bad angle I get a bit of black.  But if things are running right and you are pushing, you should only have to wipe off the smoke with a clean rag.  This is all asuming that you have clean material to work with.  Old aluminum likes to absorb things over time and no matter how much prep you give it, it will still show it's age when you weld it.Common sense in an uncommon degree is what the world calls wisdom.