Magnesium Alloy Sheet Welding Process And Arc Length Control

Because of the characteristics of low density, high ratio rigidity and ratio strength, good damping and recycle, magnesium alloys are praised of the green engineering material, which have a widely applied prospect in the fields of automobile industry, motorcycle industry and aviation. With the extensive application to magnesium alloy structural components, the join of magnesium alloys will be developed, moreover, welding is a good methods of join.To understand through the microstructure and properties in TIG welding joints of wrought alloys, the paper explored effective ways to improve the properties of fusion welding joints of magnesium alloy. Based on the experiments of AZ31 alloy by TIG, using tensile test machine, optical microscope, SEM, XRD, EPMA and micro-rigidity meter, the mechanical properties, microstructure, fracture morphology, phase composition, element distribution were investigated. The results showed the crystal grain was more fine in the fusion than that of the base metal, and the microstructure of heat affected zone became coarse obviously, which was the danger zone of crack. By Further analyzing, it was found the welding heat-input was the main cause effect on the microstructure and properties of joint. Under the condition of penetration, with the heat input decrease, the microstructure in fusion was improved, the width of HAZ becomes narrow, and the grains size in the weld zone become fine, and the mechanical properties were increased.To adapt the change of workpiece figure, the quality of thin workpiece was controlled efficiently. Based on the investigation of the relation among the current, arc voltage and arc length in magnesium alloy sheets TIG welding, a new model based on the relationship among the current, arc voltage and arc length have been put forward, which was used to control arc length exactly. Refer to the principle of PID and Fuzzy, this article designed a kind of adaptive ALC (automatic length control) control system, and the software and hardware of arc length tracing system were established. The test showed that the new designed system broke through the limit of tradition AVC (automatic voltage control) that could not work during the low current and termination, and it solved the problem of arc length control for the magnesium alloy sheets and arc-shape workpiece. By this means, good weld bead could be get, moreover it had high dynamic response accuracy and good operation reliability.In addition, the paper analyzes the problem of high-frequency interference in TIG welding, adopts the means of shield, insulate and connecting earth to prevent high-frequency interference and achieves the good results. The paper had designed the sampling circuit which take on the positive half-wave arc voltage to the feedback information of arc length, and the results showed the sampling circuit could response the change of arc length during the process of welding.