Development of New Al-Cu Based Alloys Aimed at Improving the Machinability of Automotive Castings

Abstract

This paper presents the first part of a study aimed at improving the machinability of a new Al-Cu based alloy containing very low silicon content, and intended for automotive applications. The results reported here focus on the development of the tensile properties of the alloy. This was achieved through the improvement of both casting and mechanical properties using melt treatments, alloy element additions, and heat treatment techniques. Various alloys were prepared to investigate the effects of Sr, TiB2, Fe, Mn, Ag, Sn and Zr additions on the tensile properties in the T6-and T7-tempered conditions, the intent being to use the data obtained to select the best alloy candidates for machinability studies. The results show that the T6 treatment provides the best tensile properties. Due to the low Si content, the effect of Sr modification on the tensile properties is not pronounced. Grain refining of the melt using Al-5%Ti-1%B master alloy appreciably increases the tensile strength and ductility. Excess amounts of Fe and Mn decrease the tensile properties, particularly the ductility, by increasing the total amount of Fe-containing intermetallic phases. The addition of silver was found to improve the tensile properties and stimulate ageing. The addition of tin significantly decreases the tensile properties due to its melting during solution heat treatment. The addition of zirconium, which acts as grain refiner and forms Al3Zr dispersoids, improves the tensile properties of the Sn-containing alloys.