I have lots of experience engineering with both 6061 and 7075 aluminum. I will try to keep the properties discussion relevant to receivers. These are both age/ precipitation hardening alloys which means that mechanical properties can be highly dependent on temper, and that they can be easily overaged at elevated temperatures. I will only talk about the peak aged -T6 tempers which are most common.
6061-T6 is probably the most common aluminum produced in plate or bar and for good reason. It possesses an excellent combination of good strength, good machinability, good corrosion resistance, good weldability, acceptable formability, and good cost. It is an excellent alloy and really the jack of all trades when it comes to aluminum.
7075-T6 is a much more specialized alloy developed for airframing. Compared to 6061-T6, 7075-T6 possesses significantly higher strength at the cost of significantly reduced corrosion resistance, poor formability, and poor weldability.
To me, the significantly higher bearing strength of 7075-T6 is the primary advantage it has over 6061-T6 in AR receivers which will prevent bearing yield around the takedown pins. To me, the improved corrosion resistance of 6061-T6 is the primary advantage it has over 7075-T6 in AR receivers which is especially important in 80% receivers that will be left unfinished. However a proper Type III hard coat anodize iaw mil-a-8625 will protect both alloys well.
I have no experience with 7029.
6061-T6 is probably the most common aluminum produced in plate or bar and for good reason. It possesses an excellent combination of good strength, good machinability, good corrosion resistance, good weldability, acceptable formability, and good cost. It is an excellent alloy and really the jack of all trades when it comes to aluminum.
7075-T6 is a much more specialized alloy developed for airframing. Compared to 6061-T6, 7075-T6 possesses significantly higher strength at the cost of significantly reduced corrosion resistance, poor formability, and poor weldability.
To me, the significantly higher bearing strength of 7075-T6 is the primary advantage it has over 6061-T6 in AR receivers which will prevent bearing yield around the takedown pins. To me, the improved corrosion resistance of 6061-T6 is the primary advantage it has over 7075-T6 in AR receivers which is especially important in 80% receivers that will be left unfinished. However a proper Type III hard coat anodize iaw mil-a-8625 will protect both alloys well.
I have no experience with 7029.
