EFFECT OF ALLOY COMPOSITION ON AGE-HARDENING BEHAVIOR OF RAPIDLY SOLIDIFIED AL-MN-CR ALLOYS

Al-Mn-Cr alloys of various compositions were rapidly solidified into solid solutions of extended solid solubilities, and P/M materials were consolidated from rapidly solidified flakes by cold pressing, vacuum degassing and hot extrusion. Age hardening behavior was examined for both rapidly solidified flakes and P/M materials. Significant age hardening was observed for the alloys containing 10 mass% of Mn + Cr. However, extruded P/M materials of these alloys showed higher peak hardness than as rapidly solidified flakes. Hence, such a thermomechanical effect was observed on age hardening of the alloys containing 10% of Mn + Cr, whereas no such effect was observed for the alloys containing 7% or less of Mn + Cr. Therefore, the optimum Mn and Cr contents for age hardening of rapidly solidified Al-Mn-Cr alloys are such that the G phase, (Mn, Cr)Al12, is the only constituent phase beside alpha-Al, and thus the Al-8Mn-2Cr alloy showed the highest age hardenability.