Study On Bonding Interface Of Magnesium/Aluminum Explosive Welding Composite Plate In Hot Working Process

Magnesium alloy has great application potential in the fields of automobile,aerospace and military equipment due to its various advantages such as light weight and high strength.However,the poor corrosion resistance and plasticity severely limit its wide application.Aluminum alloy has good corrosion resistance and plasticity.It is of great significance for expanding the application of magnesium alloy to prepare Mg/Al composite plate with large area,high bonding strength,light weight,high strength,good corrosion resistance and plasticity by explosive welding.However,the explosive welding process cannot produce the thin composite plate,which limits the application range of the thicker Mg/Al explosive welding composite plate.In this paper,the Mg/Al composite plate was prepared by explosive welding process,and then it was annealed and rolled.Studying the variation of the interface and bonding strength of the composite plate in the hot working process can provide theoretical and technical support for the engineering application of the explosive welding Mg/Al composite plate to a certain extent.A large area AZ31B/6061 composite plate with high bonding strength,wavy interface and no other defects such as pores and cracks was prepared by explosive welding process in this paper.The composite plate has the bonding strength of 106MPa,which is much higher than the bonding strength of Mg/Al composite plate prepared by other processes.In order to improve the performance of the thick plate,the composite plate was annealed.When the composite plate was annealed at lower temperatures,the diffusion of interfacial elements,the adiabatic shear band and other morphologies were almost unchanged,but the hardness values on both sides of the interface were significantly reduced,effectively eliminating the work hardening.The interfacial bonding strength of the composite plate had little change,it has relatively high bonding strength after annealing at 150?/2h,reaching 110MPa.At higher temperatures,the thickness of the interfacial diffusion layer increased with annealing temperature and time,and the effect of temperature on the thickness of the diffusion layer was greater than that of time.The adiabatic shear band disappeared after annealing at 200?,but its"marks"still existed.After annealing at 250?,the"marks"of the adiabatic shear band and twins all disappeared.The interfacial bonding strength decreased significantly with the increase of annealing temperature and time due to the increase of intermetallic compounds.The suitable annealing process for the composite plate was 150?/2h.In order to expand the application range of the composite plate,rolling was carried out.The physical simulation of hot rolling of the composite plate was carried out by the plane strain hot compression,and the rolling conditions were determined to be 400?/5min preheating and the roll temperature of150?.Subsequently,the composite plate was rolled at different reduction ratios.The interfacial bonding strength decreased to 44MPa after preheating at400?/5min.However,it was restored considerably after rolling,but it was far less than that of the initial explosive welding plate.With the increase of rolling reduction ratio,the thickness of the interfacial diffusion layer of the rolled plate decreased gradually,the grain size of the magnesium side near the interface increased first and then decreased,and the interfacial bonding strength decreased first and then increased.Under the 30%reduction ratio,the rolled plate without edge cracking and interfacial microcracks whose interface was well bonded was relatively straight,and the interfacial bonding strength reached to 69MPa.Considering the actual production condition and improving rolling efficiency,the composite plate was rolled without heating the two rolls.The result indicated that the plate after rolling at 400?/5min had slight edge crack and microcrack was observed at the interface,its bonding strength was 60MPa.Increasing the preheating temperature to 450?effectively suppressed the generation of edge crack,but there was still microcrack at the interface.Moreover,the interface diffusion layer was thicker,the grain of magnesium side was larger,and the bonding strength was lower.Rolling at 450?,with the increase of preheating time,the edge crack of the rolled plate disappeared gradually,the thickness of the interfacial diffusion layer increased,the grain size of the magnesium side increased,and the bonding strength decreased.However,after 15 minutes of preheating,the delamination phenomenon appeared in the rolled plate.Finally,the variation of microstructure and bonding properties of the annealed plate during rolling process were studied.The results indicated that the rolled quality of the annealed plate was better than that of the initial plate and there was no edge crack.After hot rolling of the plate annealed at 200?/2h,there was no microcrack at the interface and the interface bonding was still good.There were a lot of longitudinal cracks at the interface of plate annealed at300?/2h after rolling,and the transverse cracks propagated along the Al₃Mg₂layer.The interfacial bonding strength of annealed plate after preheating all decreased significantly.It was restored considerably after rolling,but it was lower than that of annealed plate.Just using the thickness of the interfacial diffusion layer as a criterion for judging the interface bonding strength was limited,it was also necessary to consider the size and morphology of the grain in the diffusion layer.After hot rolling of annealed plate at 300?/2h,the Al₃Mg₂phase and the Mg₁₇Al₁₂2 phase were both columnar crystal morphology,the stress was concentrated in the Al₃Mg₂ diffusion layer,and the proportion of the small angle grain boundary in the Al₃Mg₂ layer was relatively large,cracks were easily produced in the Al₃Mg₂ layer.