Influence of abnormal structure on the reliability of squeeze castings

Influence of the abnormal structure, such as coarse α phase, scattered chill structure or cold shut, in Japanese Industrial Standard (JIS) AC4CH (Al-7.3%Si-0.3%Mg) aluminum alloy squeeze castings on the reliability of mechanical properties was investigated. The shot time lag (STL) and the heat transfer coefficient between molten alloy and shot sleeve were changed as the process parameters to control the formation of the abnormal structure. Two types of sleeve lubricants, conventional oil-soluble lubricant and new-developed high insulating powder lubricant were used to control the heat transfer coefficient. Both the tensile strength and its reliability were remarkably improved by using the powder lubricant or by decreasing the STL. Regarding the fracture elongation, the average elongation was improved due to the reduction of abnormal structure on the fracture surface. However, the reliability of the fracture elongation was sufficiently improved by neither STL nor the type of lubricants. It is found that the reduction of abnormal structure is effective to improve the strength and fracture elongation of squeeze castings. In order to improve the reliability of these mechanical properties, it will be necessary that the width of the scattering of the abnormal structure size should be decreased.