Chill-cast aluminium alloy pistons mfr. - using directional solidification to obtain fine structure and high fatigue strength

摘要

The parent patent described the prodn. of castings, esp. Al or Al-alloy pistons for internal combustion engines, using a round mould with an outer insulating jacket and a base-plate plus, if required, a core suspended in the mould. The melt solidifies from the base-plate due to indirect cooling and, after an adequate solid layer is formed, direct cooling is applied to the bottom of the casting. In the present invention, a limited, dosed amt. of molten metal at the correct temp. flows into the mould followed by heat-extn. at constant speed independent of the casting height so the temp. gradient in the solid layer near the junction with the molten metal remains constant. Provides directional solidification along the axis of the piston so a fine-grained structure is obtd. which, after heating for 5 hours at 230 degrees C gives an increased fatigue strength of 10.5-13 kp/mm2.