Steel would be better, but stainless even better still (not quite as good as nichrome, but similar). Steel is solderable, aluminum and stainless not so much.
Even assuming a good bond, conductive metals like aluminum and copper make very poor resistors. For most frequencies (over ~kHz, usually), and shapes of conductor, the inductive reactance is several times the resistance. If you're only ever measuring DC, that doesn't matter, but any little transient or ripple will dutifully be transmitted to your sensitive shunt measuring circuit.
Tim