《日本钢铁协会》Vol．55（2015），No．12，P2667—2676 氢对弹簧钢疲劳性能的影响

为了提高弹簧钢的强度级别、减轻弹簧钢的重量，则提高腐蚀疲劳性能是最重要的任务。本文研究残余应力、腐蚀坑深度、氢含量对双喷丸和三喷丸试样的旋转弯曲疲劳性能的影响，得到如下结果：（1）对于人工腐蚀坑深度为250um的试样，无论是含氢或不舍氢，三喷丸都明显地提高疲劳极限；（2）对于含氢试样，夹杂物鱼眼疲劳开裂通常是疲劳断裂的起源；（3）无论人工腐蚀坑的深浅如何。喷丸试样的疲劳极限与人工腐蚀坑底部的残余压应力之间具有很好的对应关系。

Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

Ti-6Al-4V alloy(Ti64)and SUS316 L stainless steel rods were dissimilarly friction welded.Especially focusing on the detailed observation of interface microstructural evolution during the friction welding(FW),the relationship between the processing conditions,weld interface microstructure,and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L.A higher friction pressure produced a lower welding temperature in the FW,hence suppressing the thick intermetallic compound layer formation.However,hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate,high rotation linear velocity and high outward flow velocity of the Ti64.These harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’mechanical properties.The rotation speed reduction and liquid CO2 cooling during the entire processing decreased the temperature increasing rate,rotation linear velocity and outward flow velocity of the Ti64 at the weld interface periphery.Therefore,they suppressed the formation of the harmful mechanically mixed layers,facilitated the homogeneous and sound interface microstructure generation,and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.

Effect of Stacking Fault Energy on the Grain Structure Evolution of FCC Metals During Friction Stir Welding

The effect of stacking fault energy(SFE) on the grain structure evolution of face-centered cubic metals during friction stir welding was investigated by using pure aluminum,pure copper and Cu-30 Zn alloy as experiment materials.Tool "stop action" and rapid cooling were employed to "freeze" the microstructure of the flowing materials around the tool.Marker materials were used to show the streamline of the material flow.The microstructures of the three materials at different welding stages were contrastively studied by the electron backscatter diffraction technique.The results show that at the material flow stage,as the SFE decreases,the grain structure evolution changes from the continuous dynamic recrystallization to discontinuous dynamic recrystallization,and further to the dynamic equilibrium between the annealing twinning due to thermally activated grain boundary migration and the twin destruction during the plastic deformation.Owing to different grain structure evolution mechanisms,the grain structure at the end of the material flow is greatly different.Especially in copper,a lot of dislocations remain,which gives rise to the static recrystallization occurring during the subsequent cooling stage.