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The development of air-conditioners using CO2 refrigerants in place of freon-based refrigerants is underway. In these air-conditioners, the temperature of the heat-exchange cycle increases to 453 K [1]. The intergranular corrosion susceptibility of the Al-Mn-Cu alloy was investigated using the anode galvanic dissolution test after performing brazing and heat treatment at 453 K. The intergranular corrosion susceptibility was dependent on the amounts of Mn and Cu, and heat treatment at 453 K resulted in an increase in the intergranular corrosion susceptibility. In the case where brazing was not followed by heat treatment at 453 K, TEM observation revealed Al-Cu intermetallic compounds with Al-Mn precipitates on the grain boundary. On the other hand, when heat treatment was carried out at 453 K, the growth of both Al-Cu intermetallic compounds and their precipitates was observed on the grain boundary with no Al-Mn precipitates.

A new heat-resistant magnesium alloy (hereafter referred to as “ACM522”) for die-casting based on the Mg-Al-Ca-RE system has been developed by Honda R&D Co. In the 150°C temperature range, the ACM522 alloy yields high creep resistant characteristics which are superior to the conventional AE42 heat-resistant magnesium alloy, and it also exhibits an excellent resistance to both heat and corrosion which can be favorably compared with the A384 general-purpose aluminum alloy. The use of magnesium for oil pans has raised a number of issues such as reduced axial force in the bolted areas and, until now, oil pans made of magnesium had not reached the stage of commercial viability for mass-produced automobiles. The authors applied the ACM522 alloy to develop light-weight oil pans which are 35% lighter than conventional aluminum oil pans.