Gas pick-up and porosity formation in strontium-modified AC4CH alloys

Abstract

Effect of strontium addition on the gas pick-up and porosity formation in AC4CH alloys have been investigated. The alloys melt were held in the controlled humidity. It has been demonstrated that the gas pick-up occurs from the reaction between the moisture in the atmosphere and the aluminum melt rather than the reaction between the moisture and the strontium. There is less strontium loss in the moist argon atmosphere than in the noncontrolled atmosphere. The loss of strontium and the gas pick-up proceed faster in the melt of secondary alloy ingots than of new alloy ingots. Consequently much porosity is observed in the conical casting from a secondary alloy melt. Conical castings modified with strontium are more prone to exterior shrinkage in the case of lower gas content. However, the higher the gas content, the more gas pores are formed, thus reducing the volume of interior shrinkage.