Aluminium bolts are usually given a much lower torque rating for the same crank/BB set up than for steel or Ti bolts.
Something to bear in mind
Alloy crank bolts are only retaining bolts, you need to torque down the crank onto the spindle with a steel bolt, then remove it and replace with your alloy bolt.
Alloy crank bolts are only retaining bolts, you need to torque down the crank onto the spindle with a steel bolt, then remove it and replace with your alloy bolt.