孔洞缺陷对高铁动车组铝合金齿轮箱疲劳性能的影响

Effects of Porosity and Pinhole Defects on Fatigue Properties of AlSi7Mg Alloys

对于铸造铝合金,内部疏松和针孔等孔洞缺陷一般难以避免,它是导致疲劳破坏的主要原因之一。通过对铸造铝合金高铁齿轮箱疲劳性能的研究,结果表明:远离试样表面的疏松对试样的疲劳断裂影响较小,当疏松靠近试样表面时,会成为明显的疲劳裂纹源;疏松的尺寸越大或形状越不规则,越容易产生疲劳裂纹。对针孔缺陷的试验研究表明:随着针孔缺陷射线等级的增加,轴向R=0.1下的疲劳极限逐渐降低,针孔缺陷射线为2~3级时,疲劳极限约为70 MPa,针孔缺陷射线为7~8级时,疲劳极限降为50 MPa。在实际生产过程中,通过采取低压铸造工艺,加强精炼除气,提高铸件冷却速度等措施,可有效避免疏松和针孔的产生,从而提高产品的疲劳性能。

It is difficult to avoid porosity and pinhole defects in cast aluminum alloys,which is the main cause of fatigue failure.Through the investigation on the fatigue properties of cast aluminum gearboxs for high-speed trains,it is shown that the size,shape and position of porosity defects have a significant influence on the initiation of fatigue cracks.The porosity defects away from the specimen surface have a small effect on fatigue fracture while the porosity defects near the surface tend to become fatigue crack sources.The larger and more irregular porosity defects are,the more easily the fatigue cracks form.In addition,pinhole defects were also investigated.The results show that with the increase of the grade of pinhole defects by X ray detection,the fatigue limit under axial R=0.1 gradually decreases.When the grade of pinhole defects is 2~3,the fatigue limit is about 70 MPa,and when the grade of pinhole defects is 7~8,the fatigue limit drops to 50 MPa.In the actual production process,employing low-pressure casting technology,enhanced refining degassing,and increasing cooling rate can effectively reduce the formation of porosity and pinhole defects,so as to improve the fatigue performance of the products.