Fatigue Properties of Overaged Cast Aluminium-7Silicon-0.3Magnesium Alloy

Over the years, Al-7Si-Mg alloys are used because of their excellent castability, high weight-to-strength ratio, good corrosion resistance and good weldability. In this paper, the fatigue behaviour of Al-7Si-0.3Mg alloys, conforming to A356, has been studied. Specimens of this material were fatigue tested in both the as cast condition, solution treated and aged conditions. The fatigue test was conducted using 3-point fatigue bending setup with the principle of low cycle fatigue failure mechanism. Overaging is found to affect the fatigue behaviour of Al-7Si-0.3Mg alloys. The fatigue properties of as cast alloys showed a three times increase upon solution treatment. Peak ageing condition further improves the fatigue value. Exposure to severe overageing conditions reduced the fatigue properties somewhat from that of the peak values but still maintained higher value than the as-cast conditions, which is constant irrespective of the overageing condition. The improved fatigue properties of heat treated samples can be generally attributed to the spheroidisation of acicular silicon particles.