Influence of Modification on the Solution Heat-treatment Response of Cast Al-Si-Mg Alloys

Abstract

A preliminary investigation has been conducted to evaluate the influence of Sr modification on the solution heat-treatment response of hypoeutectic Al-Si-Mg (A356.0) alloys. Modified and unmodified test castings were produced in zircon-coated steel moulds and were solutionised at a constant temperature for varying times. The microstructural changes in the Si-particle morphology were analysed as a function of solution time. Machined samples were obtained from test castings to determine the tensile properties. The results indicate that the solution treatment is accompanied by spheroidisation and coarsening of Si particles. The kinetics of spheroidisation are much higher in modified than in unmodified samples. Because of the diversity in particle size distribution, however, greater coarsening rates are observed in unmodified specimens. The tensile properties of the casting increase with the duration of solution treatment and upon modification of the melt. The effect of modification is to lower the solution time necessary to obtain the desired mechanical properties in the casting.