Microstructural evolution and tensile properties of al–20 wt%Mg2Si–0.2 wt%Ba composite solidified under different cooling rates

Abstract

In recent year, Al–Mg₂Si composite becomes a topic to be discussed whether there is a potential to replace common automotive material, Al–Si in applications like piston and brake disk. However, the course with a sharp corner of primary Mg₂Si act as the stress concentration promote the initiation of crack to propagate, resulting in low mechanical and tribological performance. Hence, modification of Mg₂Si particles in Al–Mg₂Si composite is a prime concern. In the current work, the impact of cooling rates on the modification primary Mg₂Si crystal shape in 0.2 wt% Ba modified Al–20%Mg₂Si composite was evaluated. With mould preheating in different temperatures, the cooling rate was controlled. When the mould temperature is lowered, the cooling rate is increased which causes primary Mg₂Si crystal formation with different structures due to Ba atoms adsorption on {100} facets of Mg₂Si crystal which can be considered as external factors strengthening. Once the temperature of mould reduced from 600 °C to 400 °C, 200 °C and lastly to 25 °C, the primary Mg₂Si morphology changed from octahedral to truncated octahedral, truncated cube and finally to a cube respectively. Tensile results showed that Al–20%Mg₂Si-0.2%Ba composite solidified in the mould with temperature of 600 °C, the values of UTS and El% are higher than other composites solidified in other mould temperatures. Furthermore, the tensile fracture surface of Al–20%Mg₂Si-0.2%Ba composite solidified in the mould with temperature of 600 °C depicted less decohesion and debonding of the primary Mg₂Si particles in the aluminium matrix together with fine dimples on the fracture surface which elucidate the ductile fracture mechanism. The size and structure of the primary Mg₂Si in the Al–Mg₂Si composite can be regulated by using this practical, affordable approach, leading to the use of this composite in industrial products.