Influence of the Ceramic Reinforcement on the Fatigue Strength of the Aluminum-Matrix Composites Subjected to Electrodischarge Machining

摘要

The materials examined were the composites with an Al+20%Si+3%Cu+1%Mg matrix reinforced with 5% of Al_2O_3, SiC or Si_3N_4 particles. The composites were produced by powder metallurgy using hot extrusion. The samples intended for fatigue tests were cut off composite rods using an electricdischarge machine tool equipped with a 0.25 mm brass wire which functioned as the electrode (WEDM). Fatigue tests were conducted under pulsed tension. Samples of the same materials, but prepared by traditional methods, i.e. by grinding, were also tested for the sake of comparison. The samples machined by the electrodischarge method had lower fatigue strength than the samples subjected to grinding. This is related with the different states of the surface layer. After the WEDM machining, the surface layer, a dozen or so micrometers thick, has a fine-crystalline structure with hardness higher than that of the material beneath, it is porous and occasionally contains microcracks. The highest fatigue strength was shown by the composite reinforced with SiC particles.