Research On The Isothermal Composite Extrusion Technology For Mg/Al Bimetal And Microstructure Property

Based on Deform 2D finite element simulation software, composite extrusion of 1100 aluminum and AZ31B magnesium bimetal alloy under different process parameters were analyzed, including the deformation, temperature field, value change of damage, equivalent stress and strain distribution, stroke-load relationship in the process and so on. Through the study of maximum damage, extrusion load and temperature distribution in the process of simulation, found that the extrusion speed and die temperature have greater influence on extrusion forming, within the scope of 1-5 mm/s, as the extrusion speed increased, maximum damage showed a trend of increase with the decrease in the first and temperature rise significantly increased, and with the extrusion temperature increased, maximum damage showed a trend of decrease. And the lower of the extrusion temperature in the process of extrusion, the greater the extrusion temperature rise. And the extrusion temperature and speed have no significant influence on the forming load.Based on the simulation analysis results, the maximum damage and temperature distribution in the process of the forming as the evaluation index, the forming process parameters for extrusion rate of 2 mm/s, extrusion temperature 470℃ were obtained.Under the process parameters, A1/Mg bimetal composite extrusion experiment was carried out, it is concluded that the A1/mg composite extrusion rod has continuous outer composite, and with no obvious defects.Scanning electron microscopy(SEM) and energy dispersive spectrometer (EDS) were used in the analysis of A1/Mg composite combined interface, the results show that interface reaction layer generate in the A1/Mg alloy contact area, with thickness of about 400 um. The new phase of Mg17Al12 generates close to the side of AZ31B magnesium alloy substrate of interface layer, generates a new phase of Al3Mg2 in the side of the 1100 aluminum substrate. Electron back scattering diffraction (EBSD) test results shows that the average grain size of Mg17Al12 phase is 3-20 um, the average grain size of Mg2Al3 phase is about 3-10 um, the outer aluminum substrate has obvious processing and texture with uniform orientation, and the grain size in outer layer is not uniform and with different grain orientation, which shows that the composite interface is formed after the diffusion reaction, and the grain grew in random. Partial recrystallization can be seen on the grain boundary of new generation phase.The shear experiments result of combined interface shows the interface shear strength is about 23.4 Mpa. Both sides of the combine interface were analyzed by X ray diffraction (XRD) and energy spectrum after shear fracture, the Mg2Al3 phase was found on both sides of the fracture, which can show that the fracture happened in Mg2Al3 layer, and microhardness test results show that near the interface bonding area, the average hardness of AZ31B magnesium alloy is about 55HV, hardness of aluminum 1100 average is about 30 HV, and the new generation of Mg17Al12 phase layer’s hardness is about 170HV, the average phase Mg2Al3 layer hardness is about 210 HV. So the Mg2Al3 layer hardness is the highest hardness layer interface, and also is the brittle area layer.