On the Elevated-Temperature Strengths of Some Aluminium Cast Alloys for Piston

This investigation was carried out in relation to the effects of heat-treatment and nickel content on the tensile properties, creep and fatigue strengths, at the temperature ranging from room-temperature to 400°C on AC5A (Y alloy), AC8A (Low-Ex.) and AC8B (Alcoa D 132) cast aluminium alloys for piston.The chemical compositions and mechanical properties at room-temperature including the heat-treatments are given in Table I and II, respectively. The specimens were cast into a permanent mould which is in accordance with Japanese Industrial Standard (JIS) H0321.The alloys were compared on the basis of their tensile properties at elevated-temperature after 1000 hour soaking. The creep tests were carried out with the lever-type creep-rupture tester, and the creep strengths were calibrated at 0.1% per 1000 hours. The fatigue tests were conducted on Ono's high-temperature fatigue tester (3000rpm) and fatigue strengths were determined at 107 cycles.The fatigue strength showed lower value at the temperature ranging from room-temperature to 300°C than yield strength. In the case of AC8A and AC8B alloys, however, the creep strength showed the lowest value of the temperature above 200°C. As for the effect of heat-treatment conditions on their strengths, higher values were given by T6 treatment at the temperature up to 200°C, and T5 treatment showed slightly higher strengths than by other treatments at further elevated-temperature. The authors would recommend T5 treatment for the heat-treatment of those alloys for piston.The strengths of nickel-free alloys decreased a little compared with nickel-containing alloys at elevated-temperature. It would appear from the above results that elimination of nickel from the alloys is undesirable. Alcoa F132, however, which has a reduced nickel content of less than 0.50%, is currently in use in U.S.A., and in consideration of the difference in strengths of nickel-free and nickel-containing alloys, it may be acceptable for nickel content of these alloys to approach the lower limit of the current specification.