Effect of Die Orientation on the Mechanical and Physical Properties of 356 Aluminium Alloy Castings Produced by Gravity Die Casting

Abstract

Al–Si–Mg alloys are widely used in automotive and aerospace applications due to their excellent castability and mechanical properties. Gravity die casting (GDC) is commonly employed to manufacture such components. While AISI H13 tool steel is typically preferred for GDC dies, mild steel dies may be used for low-volume production because of their lower cost and ease of fabrication. However, mild steel dies generally exhibit limited-service life due to lower hardness, reduced wear resistance, and poor thermal fatigue resistance. Therefore, optimisation of casting parameters is necessary to improve casting quality. This study evaluates the influence of die orientation and pouring temperature on the mechanical, physical, microhardness, and porosity characteristics of aluminium (Al) alloy 356 castings produced using an ASTM A36 mild steel gravity die. The casting process was conducted at different pouring temperatures using vertically oriented casting (VOC) and horizontally oriented casting (HOC) configurations. The resulting castings were evaluated through impact testing, microhardness measurements, and porosity analysis, including apparent porosity (AP) and bulk porosity (BP). Results show that VOC at a pouring temperature of 900 °C improved impact toughness by 59.3% (average 16 kJ/m²) compared with HOC, while reducing surface microhardness by 2.4% (82.7 HV). Additionally, VOC significantly reduced BP by 91.9% and AP by 69.5%. Compared with castings produced at 800 °C, VOC at 900 °C increased impact toughness by 34.3% and reduced BP by 75.15%. Overall, vertically oriented casting using mild steel dies significantly improves impact toughness and reduces porosity in 356 Al alloy castings.