| Magnesium alloys have characteristics such as high specific strength,low density,excellent electromagnetic interference shielding property,high thermal conductivity and easy recyclability.They offer a promising potential for use in automobiles,aircrafts and military weapons.However,components of magnesium alloys are susceptible to wear and damage over time and reach their “end of life” stage prematurely due to their poor wear resistance and poor corrosion resistance.Cladding,as an important way of remanufacturing,has emerged as an effective practice to restore shape and functionality of damaged components,thus prolonging the service time of the damaged components and greatly reducing the cost.This paper explored the feasibility and application of CMT in cladding of magnesium alloys.Firstly,the effects of CMT welding parameters on welding stability were investigated.Secondly,the effects of heat input on the microstructures and properties of cladding were studied.Lastly,a successful multi-pass cladding of magnesium alloy was achieved employing the optimized CMT welding parameters.Since synergic CMT welding program for magnesium alloy filler was not available,claddings were conducted employing the Al synergic CMT welding program.The results showed that the stability of CMT welding deteriorated with the increase of wire feed speed(WFS).For DC-CMT,the welding process was stable and spatter-free when the WFS was no more than 5 m/min,while for pulsed-CMT,the welding arc was stable when the WFS was no more than 4 m/min.Repelled droplet transfer was observed at a higher WFS.It was speculated that molten droplets deviated from wire axis under the influence of the recoil force originated from the evaporated magnesium atoms,compromising welding stability.Under pulsed-CMT mode,WFS of 4 m/min could obtain stable welding process and favorable wetting condition of claddings,suitable for the multi-pass cladding of magnesium alloys.When pulsed-CMT with WFS of 4 m/min was employed,the weld zone(WZ)consisted of α-Mg and β-Mg17Al12,and massive grain growth,coarsened grains boundaries were found in the heat-affected zone(HAZ).Multiple pores were witnessed in the WZ at a welding speed no lower than 14mm/s,while liquation cracks were observed in HAZ at a welding speed no higher than 8mm/s.Due to the local melting in HAZ,eutectic α-Mg contained more Mg and less Al compared with α-Mg,however,in WZ eutectic α-Mg contained less Mg and more Al compared with primary α-Mg.Under pulsed-CMT,the optimized CMT welding parameters for multi-pass cladding of magnesium alloys were WFS of 4 m/min and welding speed of 12 mm/s.Under the optimized welding parameters,when the distance between passes was set as 5 mm,good surface appearance could be obtained.Grains in the area between two passes greatly coarsened compared with grains in other areas of the cladding layer.Microstructures in HAZ which located between passes further coarsened,and β phases gathered together forming band shape.For β phases in normal HAZ,they exhibited dot shape.The corrosion resistance of the cladding layer was no lower than that of the base metal under pulsed-CMT welding. |
PDF Full Text Request