Development of new high strength Al-Si eutectic alloys and investigation of their fatigue properties in extra-long life range.

为寻求材料开发的最佳工艺条件，系统地研究了Al-Si共晶合金中Si相分布与力学性能的关系，并采用连铸和挤压两种工艺制备了拉伸试样，得到以下结果：（1）热处理影响基体硬度，但不改变Si相分布; (2)抗拉强度σ v与基体的维氏硬度H_v成正比。(3)最大Si相的尺寸（* 面积_<max>）对塑性σ_f的影响最为关键。为了研究Si相对Al-Si共晶合金在长疲劳寿命区（N*10^7）和超长疲劳寿命区（N&gt;10^8）疲劳性能的影响，进行了拉压疲劳试验。得到的结果是：（1）在挤压变形条件下，超长寿命的疲劳断裂机制为剪切型，与长寿命时断裂起源于Si相的疲劳断裂机制不同。(2)在连铸情况下，所有的疲劳断裂都是由剪切型裂纹引起的。(3)在挤压条件下，疲劳极限可用面积参数模型预测，即用<max>Si相的面积和H_v两个参数来预测。

To find the optimum conditions for the material development, the relationship between Si-phase distribution and mechanical properties of Al-Si eutectic alloys in terms of production factors was systematically investigated.Tensile test specimens were prepared from two materials produced by two different processes, continuous casting and extrusion.The obtaind results are : (1) Heat treatment influences the matrix hardness without changing Si-phase distribution. (2) Ultimate tensile strength siguma v is proportional to Vickers hardness H_v of Al matrix. (3) The size(*area_<max>) of the maximum Si-phase has a most crucial effect on ductility epsilon_f.In the next step, to investigate the effect of Si-phase on fatigue properties of Al-Si eutectic alloys in long fatigue life range (N*10^7) and extra-long fatigue life range (N>10^8), tension-compression fatigue tests were carried out. The obtained results are : (1) In the case of extrusion, the fatigue fracture mechanism in extra-long life was shear type and different from that in long life in which the fracture origin was at Si-phase. (2) In the case of continuous casting, all the fatigue fractures were caused by shear type cracking.(3) In the case of extrusion, the fatigue limit can be predicted by the *area parameter model, i.e. with two parameters, the *area_<max> of Si-phase and H_v.