Abstract
A basic study has been made on the heat-resistance of chill-cast Al-4 mass%Cu-(0-6) mass%Mn alloys, by examining hardness and structural changes mainly at an over-aged state. The cooling rate during solidification was estimated at about 103 K·s−1, and nearly all of Mn atoms seemed to dissolve in the supersaturated solid solution for chill-cast specimens containing Mn up to 4%. It was revealed that softening due to over-aging became markedly suppressed as Mn content increases for specimens pre-treated (homogenized at 793 K for 0.6 ks, water-quenched, aged at 473 K for 60 ks) and then subjected to the over-aging treatment at 623 K. This was attributed to the fact that the number of ternary precipitates formed during over-aging increases with increasing Mn content, and that these precipitates did not easily coarsen due to the low diffusivity of Mn atoms. Alloys containing Mn more than 2% were considered to show superior heat-resistance to that of 2219 alloy. Aging at 473 K for 60 ks without homogenization was a more effective pre-treatment for suppression of softening in high Mn alloys.
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