STRONTIUM MODIFICATION OF ALUMINUM-ALLOY CASTINGS IN THE EXPENDABLE PATTERN CASTING PROCESS

The influence of strontium modification on microstructure, pore charac teristics and tensile properties of Al-Si-Cu castings produced by the expendable pattern casting (EPC) process has been investigated. Test c astings have been produced at strontium concentrations varying from 0. 0004%-0.03%. The castings have been analysed by microscopic and image analysis techniques. The results indicate that optimum strontium conce ntrations are between 0.01% and 0.015%. A coarsening of silicon partic les is observed at strontium concentrations greater than 0.015%-0.02%. The addition of strontium to the melt also refines the iron- and copp er-bearing phases in the casting. The amount of bulk porosity, average pore size and tensile properties of modified EPC castings are compara ble to green sand castings. EPC castings are prone to surface porosity . Strontium modification has a significant effect on the pore distribu tions in EPC castings. The overall porosity and the maximum pore size increase with strontium modification.