Specimens of A356 Al/SiCw and A390 Al/SiCwmetal matrix composites (MMCs) were produced by squeezecasting and tested under fully reversed high cycle fatigueconditions at room temperature. A staircase method wasemployed to determine the mean fatigue strength at 107 cycles.The presence of 17vol.% SiC whiskers in the A356 Al alloyincreases the fatigue strength by 29%. In contrast, the A390Al/SiCw composite, containing identical whiskerreinforcements, showed very little improvement of fatiguestrength when compared to the matrix alloy. An analysis of thefracture surfaces of both composites shows that fatigue cracksinitiated primarily at pre-existing regions within the preformswhich are characterized by the absence of the SiC whiskers.The reinforcement-free regions take two forms: continuous"veins," which are very deleterious to fatigue, anddiscontinuous "unreinforced regions," which are deleteriousonly in certain geometries. An analysis is presented torationalize the geometry effect. Finally, we also identify theimportance of large primary Si particles in limiting fatigue lifeof the A390 Al materials.
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机译：通过在室温下完全反转的高循环脂肪屈服，通过挤压和测试A356 Al / SiCw和A390 Al / SiCwometal基质复合材料（MMCs）。楼梯方法施用，以107个循环确定平均疲劳强度。A356 Al合金中的17℃的存在。％SiC晶须的疲劳强度疲劳强度为29％。相比之下，含有相同的WhiskerreInforcements的A390Al / SiCW复合材料，显示与基质合金相比的疲劳率的改善很小。两种复合材料的分析表明，主要在预制率内的预先存在于预甲晶内的预先存在下的疲劳裂缝的特征在于，无晶须的缺失是缺乏两种形式：连续的“静脉”，这是非常有害的“静脉”疲劳，anddiscontion“未使用的地区”，在某些几何形状中是革而代的。提出了一种分析，将几何效应倾斜化。最后，我们还确定了大型初级Si颗粒的Idipportance，以限制A390 Al材料的疲劳寿命。
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