Effect of oxide film defects generated during mould filling on mechanical strength and reliability of magnesium alloy castings (AZ91)

Abstract

The influence of new oxide film defects generated during mould filling on the mechanical strength and reliability of magnesium alloy castings (AZ91) has been investigated. The filling behaviour was evaluated using an optical video camera. Three point bend tests were conducted on specimens cut from the cast plates. The Weibull statistical method was employed to quantify the scatter of mechanical properties. Scanning electron microscopy and energy dispersive X-ray techniques were used to observe features of the oxide films on the fracture surfaces. Results indicated that there is a critical in-gate velocity that lies between 0·25 and 0·35 m s⁻¹. Thin and folded surface oxide films were observed at the fracture surfaces. These films are likely to be distributed throughout the casting due to the random nature of the entrainment process. It was found that the presence of new oxide films strongly affects the scatter of the mechanical properties of the castings.

Keywords:

• AZ91 alloy
• Filling behaviour
• In-gate velocity
• New oxide films
• Mechanical properties and reliability