The Analysis Of CMT Weldability For Dissimilar Metals Between Magnesium Alloys And Pure Copper By

In modern engineering industries, the use of welded structures of dissimilar alloys can not only make full use of the properties of the materials, but also save rare metals and reduce the cost of the entire structure. Magnesium and Magnesium alloys have low density and low strength good rigidity good measurement stability Then this joint may have a broad application prospect in the mechanical, chemical, transportation, aerospace, nuke industry,oil equipment engineering fields, etc. Copper and copper alloys have excellent electric and thermal conductivity, good cold and hot working performance, high oxidation resistance have a broad application prospect in electric, corpuscle, power, transportation, aerospace and war industry engineering fields, etc. So the hybrid structure of Mg/Cu dissimilar alloys is an attractive design in this field.The dissimilar materials, magnesium alloy AZ31B and pure copper T2were lap joined by cold metal transfer (CMT) welding technology. Firstly, The CMT brazing-welding joining was carried out using TPS-3200type CMT welding procedure. The influence of various variables including wire feed speed, welding speed, welding current and voltage on the weld appearance and mechanical property and the wires with various compositions were investigated. Secondly, in order to understand the bonding mechanism between these two materials, the microstructures of the welded joints were observed and analyzed by scanning electron microscopy (SEM), X-ray diffractometer (XRD).The experimental results showed that:As shown,welding variables such as wire feed speed, welding speed, welding current and voltage have a significant effect on the weld appearance and mechanical property of the joints. Satisfied joints with good weld appearance and higher mechanical property could be achieved by the optimized welding parameters. It was found that the joints were composed of a welding joint on the magnesium side and a brazing joint on the Copper side. The welded joint on Mg side was composed of the weld metal formed molten Mg base metal, and molten Mg wire, and heat affected zone. The brazed joint on Cu side was formed by weld metal and Cu base metal. The weld metal was mainly composed of a-Mg solid solution, skeletonized phase Mg17Al12,Brazing interface phase composition is more complex.The head and tail end of Brazing interface named A and c zone Due to the effect of thermal diffusion of the copper atoms to form a layer of intermetallic compounds. Its composition is mainly Mg17Al12+α-Mg+Mg2Cu. The thickness of the layer of intermetallic is about40μm, The central regions of the brazing interface B area due to the heat input is very large, Copper melting many to form the second intermetallic compounds.is mainly MgCu2+Mg2Cu+Al6Cu4Mg5.the shape is white squares. When the wire feed speed is less thanll.Om/min, Intermetallic layer of magnesium copper connection and welded joint mechanical properties play a key role In addition, coarse grains occurred at HAZ of Mg base metal due to heat input during the welding process. When the wire feed speed is greater than11.0m/min Because of the increased amount of copper melting main component is MgCu2brittle phase full of weld lead to lower weld strength. Through the weld hardness testing, the fusion line area and intermetallic compound layer area is the lowest parts of the welded joint strength. Through on the tensile fracture of welded joint microstructure and phase composition of the fracture analysis on fracture occurs mainly on the weld end the fusion line, the welding and brazing interface of intermetallic compound layer. By using nickel aluminum bronze wire weld mechanical properties of welded joint is not high, only up to about1.2KN, use AZ92and AZ61magnesium wire welding, the mechanical properties of welded joint is very good and stable, the highest can reach1.8KN, for about95%of the parent metal performance. Using magnesium nickel aluminum bronze wire and two kinds of welding wire for3mm thick magnesium copper welded joint mechanical properties of butt welding income is stronger, is about three times the butt welding of left and right sides.