IMPACT OF Mg ON DIVERSE PROPERTIES OF EUTECTIC Al - Si AUTOMOTIVE ALLOY

Abstract

Magnesium is an important element for alloying in the composition of Al - Si automotive alloy to enhance mechanical properties and ensure optimum performance. A systematic investigation has been carried out to observe its effect on various properties of this alloy. Investigations include age hardening, thermal conductivity, tensile, wear, corrosion, fracture as well as microstructural properties by developing two Al - Si automotive alloys with and without 0.5 wt. % Mg. Experimental results confirm that both alloys improve its strength during thermal ageing treatment through development of clusters and GP zones alongside metastable phases and maximum can be achieved at around 200°C for 150 min. Addition of Mg provide the different Mg-rich precipitates resulting the better strength. Mg addition in this level improves hardness but reduces the thermal conductivity of automotive alloys by approximately 15 %. Again, the tensile strength improved significantly with a reduction in ductility by 20 % mutually. These Mg - rich intermetallic precipitates improve wear properties by 30 % in dry sliding conditions but suffer 60 % in corrosive environments. Once exposed to an acidic environment, the corrosion rate is elevated by 50 %. Microstructural study confirms plate-like eutectic Si phase and the higher intermetallic created by Mg as coarsen the grain boundary. After being subjected to a temperature of 350°C for 1h, alloys achieve a totally recrystallized state. Fractography of Mg added alloy shows severe breakup occurred at its intermetallic along with a cleavage pattern featuring flat facets indicative of the Al - Si eutectic zone.