基于二次枝晶间距的差压铸造A356铝合金疲劳寿命预测

Fatigue Life Prediction of Counter Pressure Casting A356 Aluminum Alloy Based on Secondary Dendrite Arm Spacing

差压铸件由于复杂的结构、凝固条件不均匀,其内部的二次枝晶间距分布存在较大差异,进而导致不同区域存在不同的性能。目前,产品设计阶段的有限元分析采用统一的材料疲劳性能模型,导致模拟与试验结果存在偏差。通过对差压铸件不同位置区域进行二次枝晶间距测量和材料疲劳试验,建立了差压铸造A356铝合金的疲劳寿命、应力和二次枝晶间距的定量关系式,得到了不同二次枝晶间距对应的S-N曲线。经过试验验证,该定量关系式的预测结果与试验结果符合较好,预测疲劳寿命的对数相对误差最大绝对值在2%以下。同时,还通过扫描电镜(SEM)对材料疲劳断口进行了观察,阐述了疲劳裂纹的萌生和扩展机制。

Due to the complex structure and non-uniform solidification conditions of counter pressure casting,the distribution of secondary dendrite arm spacing in the castings exhibits apparently difference,which leads to different properties at different areas.At present,finite element analysis in the product design stage uses uniform material fatigue model,resulting in deviation between simulation and test results.The secondary dendrite arm spacing measurement and material fatigue tests were carried out at different areas of counter pressure castings to evaluate the quantitative relationship between fatigue life,stress and secondary dendrite arm spacing of alloy,and then the S-N curves corresponding to different secondary dendrite arm spacing were obtained.Experimental tests validate that the prediction results of the quantitative relationship are in good agreement with the experimental ones,and the maximum absolute value of the logarithm relative error of predicted fatigue life is below 2%.Meanwhile,crack initiation and propagation mechanism were expounded by scanning electron microscopy(SEM)observation.