I'm considering making a set of these for my own cars. I'm a machinist and have access to an engineer who is a car guy at work. His recommendations: First was use chrome-moly (4130 or 4140) tubing. However I'm not a welder and asked about aluminum as an alternative. His recommendation was to compare the tensile strengths of the materials and then adjust the diameter (for cross-sectional area) of the aluminum bars to compensate for the lower tensile strength. That and make sure the threads are machined to the appropriate engagement %. So what I got for my Subaru (first car I will be trying these on) is that the stock arms are about 19mm/.750" diameter. Tensile strength of 1025 steel is rated at around 60-103 kpsi, 6061-T6 aluminum is rated at approx. 45 kpsi. So working with 80kspi for the stock arms the aluminum arms must be 1.78 times greater in cross-sectional area. So what I got was at .750" diameter the cross-sectional area is .442 square inches times 80kpsi gives me 35.36. 1.000" diameter the cross-sectional area is .785 square inches times 45kpsi gives me 35.34. Close enough. However he still wouldn't recommend these for racing and chrome-moly is still his first choice. (also use at least 5/8" alloy rod ends/heim joints)
I haven't measured my Supra's links yet so I'm not sure how much bigger the aluminum versions will have to be. Another alternative is using 7075-T6 which has a tensile strength of about 83 kpsi but is significantly more expensive.
The problem I see with these ones being offered is that the diameters of the steel vs aluminum bars looks like they are the same. This would make the aftermarket bars only 56% the strength of the stock bars (assuming they are 6061-T6). Also the diameter of the bar replacing the stamped/welded stock piece (with the holes in it) is quite a bit less, and there is also stiffness to account which I haven't got into yet.
Any thoughts?