AC4CH-based metal matrix composites with 9Al_4O_3・2B_2O_3 reinforcement have been produced using squeeze casting method, after T6 heat treatment, we evaluated fatigue life characteristics of matrix and MMC composite and investigated fracture mechanism. the results are summarized as follows. 1. T6 heat treated MMC decreased mechanical properties because of MgO・Al_2O_3 of spinal type by the reactions between whisker and small amount of Mg in the matrix. 2. Fatigue limit of MMC was a 71% higher than that of T6 non-heat treatment, fatigue strength of T6 heat treated MMC lower general. 3. In the fatigue fracture of whisker, surface of whisker before T6 heat treatment had no reacive products and damage was very small but whisker after T6 heat treatment had a lot of reactive products.
