To improve the fatigue properties of AZ31 magnesium alloys, two technical approaches were used to reform the material structure. The first approach is grain refinement of the material structure by multi-axial alternative forging MAF to reduce anisotropy and to improve the strength. The second approach created an inclined recrystallized surface layer by shot peening to retard crack initiation on the surface layer and the propagation rate in the tissue layer of the fine-grained structure. The relationship between the microstructures and fatigue properties was examined. As a result, by combining MAF and heat treatment the endurance limit increased by 15%. Moreover, shot peening at medium temperatures formed a recrystallized submicrometer grain size microstructure in the surface layer and an inclined structure to a depth of over 100 μm below the surface, and the fatigue properties increased by about 30%. From measurement of the crack propagation rate, it was found that the improvement in fatigue properties led to the delay in crack initiation in the fine-grained surface layer and decreased the crack propagation rate in the residual strained layer.

The effect of shot peening ( SP)at various temperature on mechanical properties ， i ． e ． fatigue ， tensile and bending characteristics ， fbr fine − grained AZ31magnesium alloy was investigated ． The residual stress was occurred by SP ， which was exarnined at worm temperature was higher than those ofroom temperature SP． Although elongation decreased iittle fbr this material with high residual stress ， tensile and bending characteristics improved remarkable ． Especially ， the endurance limlt of fatigue improved 22 ％ higher on comparison with that ofnon − SP material ． On the other hand ， under high temperature SP ， the material which have the graded microstructure 倉om surface to about O5mm in insides was able to be created ．

No abstract

No abstract

No abstract