Abstract
The temperature field in welded plates has a significant influence on the microstructure and thereby their properties during friction stir welding (FSW). In this work, a self-designed heat pipe with different cooling liquid was applied in the FSW process for AZ31 magnesium alloy. The temperature fields, microstructures and properties of the welded joints were investigated. The peak temperatures and the durations of high temperature at both the advancing side and the retreating side decrease during the FSW process after applying the heat pipe and adding the ambient temperature water in the condensing tank. The top part of the weld nugget zone of the joint shows a significant decrease as well as its middle part due to the cooling effect of the heat pipe. The microstructure of the weld nugget zone is refined, associated with the increase in the hardness after applying the heat pipe. When the cooling liquid turns into ice water, grains in the weld nugget zone become significantly smaller and have a more homogeneous size. The mean value of hardness increases and the corresponding deviation is declined. Therefore, these results indicate that the application of the heat pipe and the employment of ice water as the cooling liquid can further refine the microstructure and enhance the strength of the material.
Highlights
Magnesium (Mg) alloy is considered as one of the most promising potential metallic materials since it possesses several advantages including low density, high specific strength, excellent thermal conductivity and outstanding electromagnetic shielding [1,2,3,4,5,6]
AZ31 Mg alloys have become among the promising non-ferrous metal materials used in these fields due to the high room temperature strength and resistance to atmospheric corrosion [7,8]
A brittle intermetallic phase is prone to being formed during the welding process, which leads to the decrease in the mechanical properties of friction stir-welded AZ31 magnesium alloys [12]
Summary
Magnesium (Mg) alloy is considered as one of the most promising potential metallic materials since it possesses several advantages including low density, high specific strength, excellent thermal conductivity and outstanding electromagnetic shielding [1,2,3,4,5,6]. AZ31 Mg alloys have become among the promising non-ferrous metal materials used in these fields due to the high room temperature strength and resistance to atmospheric corrosion [7,8]. Conventional welding methods (such as, metal-arc inert gas, plasma arc and tungsten-arc inert gas) may lead to large residual stress, stress corrosion cracking sensitivity and evaporation loss [11]. A brittle intermetallic phase (such as β-Mg17 Al12 ) is prone to being formed during the welding process, which leads to the decrease in the mechanical properties of friction stir-welded AZ31 magnesium alloys [12]
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