Effects of microstructure on optimum heat treatment conditions in metal-matrix composites

Heat treatment conditions appear to differ in metal-matrix composites than in the matrix alloys alone. The time necessary for solutionising appeared to be much shorter in the composite primarily due to a very small grain size. The precipitates were completely dissolved in less than 1.5 min at 500 C. The normally applied T6 solutionising time of 1 h is not, therefore, necessary. Artificial ageing was not very effective in the AA2124 15 vol % SiCw composite since the precipitates nucleated and grew on the whisker interfaces. Only natural ageing was necessary to get peak tensile and yeild strength values, although a slight decrease in ductility was noticed. The rate of room temperature ageing was nearly identical in both the composite and the unreinforced alloy. 24 refs.