The best combination of strength and formability of any aluminum alloy is offered by the 5000 series (Al-Mg) alloys containing 4 to 5% magnesium, e.g. 5182. In the conventional annealed state (-0 temper) necessary for maximum formability, this alloy suffers from the formation of type A Luder lines (stretcher strains) when plastically deformed a small amount (<1%). Such Luder lines are similar to those commonly encountered in steel and are unacceptable in outer panels. The conditions under which Luder lines form are discussed. The introduction of 5182-SSF has completely avoided these problems with a stretcher-strain free (SSF) material which exceeds the formability of 5182-0.
