Effect Of Cryogenic Treatment On Fatigue Properties Of AZ61 Magnesium Alloy TIG Welded Joints

In the production practice, welding structures run under the function of variable loading in many cases. Many accidents happened frequently owing to the fatigue failure of welding joints,while there was not any forebodes and we can not take any protective measures in the fatigue cracking of materials,so it is necessary to study the fatigue failure of welding joints. The deep cryogenic treatment experiment is that the research object is placed in the low temperature environment of lower than-130℃, and in the extreme temperature can change the material organization so that to change the properties of materials, which is one of a new material strength processes.Our research team have done lots of researches on improving the performance magnesium alloy welded joint through deep cryogenic treatment. This paper went into a research on cryogenic treatment caused the influence for AZ61 magnesium alloy and TIG welded joints fatigue performance.In this paper, the research tested the impact toughness and hardness in different areas of welded joints and studied the influence on tensile properties of parent metal by welding process, tested the fatigue performance of AZ61 magnesium alloy parent metal and AZ61 magnesium alloy TIG welded joints, explored the influence to the fatigue performance of AZ61 magnesium alloy by weld thermal cycle,proceeded deep cryogenic treatment to welded joints,probed into the influence to the fatigue performance of AZ61 magnesium alloy welded joints by deep cryogenic treatment.This paper shows that, with the2×106 cycling times, the fatigue performance of the welded joints by deep cryogenic treatment increased about 14.57% than the welded joints without deep cryogenic treatment. The grain of welded joints became refined after deep cryogenic treatment, the second phase increased and its distribution became uniform, diffused, the strength of fine grain improved the strength of material. The deep cryogenic treatment rotated certain grain of the welded joints,hindered partial dislocation slipping,and improved the strength and toughness of welded joints. The fatigue fracture of welded joints changed from brittle fracture to ductile-brittle mix fracture,which can improve the ductility and toughness of welded joints.