Abstract:The effect of the low temperature treatment at -78℃and -196℃on the microstructure and properties of 18%SiCw/6061(volume fraction) Al alloy composites of as-squeeze-casting were studied. The results show that, after the low temperature treatment, the dislocation density in matrix increases, and the residual stress of the matrix decreases, as well as the tensile yield strength of the composites improves. The high residual stress exists in the matrix of the composites of as original squeeze casting. The mismatch degree between the matrix and SiCwphases increases during the low temperature treatment. The matrix undergoes the tensile plastic deformation during the cooling procedure. On the contrary, the matrix encountered an elastic unloading procedure during the heating up process from low temperature to room tempera-
ture. The increase of dislocation density and the decrease of residual stress in the matrix are the main reason of the improvement for tensile yield strength of the composites.

Key words: SiCw/6061 composites; dislocation; residual stress; tensile yield strength