The Effect Of Mg/Si Ratio On Hot Tearing Susceptibility Of Al-Mg-Si Alloys

Al-Mg-Si alloy has high specific strength,low density,good formability,excellent corrosion resistance,weldability,machinability and other excellent comprehensive performance,and has been widely used in the fields of construction,aviation,automobile and shipbuilding.At present,the research on Al-Mg-Si alloys mainly focuses on microstructure and mechanical properties at home and abroad,but there is little research on the hot tearing susceptibility.The hot tearing susceptibility of aluminum alloy is very important in the process of casting ingots before plastic forming of deformed aluminum alloy,liquid forming of cast aluminum alloy,and even in the weld solidification process of aluminum alloy solder,which is the bottleneck of manufacturing large size ingots,complex structure castings and high quality welding.Therefore,study on hot tearing susceptibility and hot tearing formation mechanism of Al-Mg-Si alloy is great significance for the preparation of Al-Mg-Si alloy with excellent comprehensive properties.In this paper,based on the Clyne-Davies theoretical model,the hot tearing susceptibility of Al-xMg-1Si（Mg/Si=1,1.4,1.73,2）alloys and Al-3（Mg+Si）（Mg/Si=1,1.5,2,2.75）alloys with different Mg/Si ratios were predicted.The predicted results were verified by the"T"type hot-crack mold test system,and the results showed that the predicted results had a consistent change trend with the experimental results,that is,the hot tearing susceptibility of Al-xMg-1Si alloys decreased with the increase of Mg/Si ratio,and the hot tearing susceptibility of Al-3（Mg+Si）alloys decreased at first and then increased with the increase of Mg/Si ratio.In this paper,the parameters of Al-xMg-1Si alloys and Al-3（Mg+Si）alloys,such as the solidification path,characteristic temperature during solidification and the change of solid phase fraction,were tested by means of double thermocouple differential thermal analysis.It was found that during the solidification process of Al-xMg-1Si alloys,the dendrite interference temperature and precipitation temperature ofα-Al primary phase decreased with the increase of Mg/Si ratio,the precipitation amount and precipitation temperature of Mg₂Si second phase increased gradually.During the solidification process of Al-3（Mg+Si）alloys,with the increase of Mg/Si ratio,the dendrite interference temperature and precipitation temperature ofα-Al primary phase first decreased and then increased,the precipitation amount and precipitation temperature of Mg₂Si second phase increased at first and then decreased.In order to reveal the Mg/Si ratio on Al-Mg-Si alloy microscopic mechanism of the hot tearing,this paper also analyzed the microstructure and fracture morphology of Al-xMg-1Si alloys and Al-3（Mg+Si）alloys hot tearing area based on the test results of XRD,SEM,EDS and DSC.The results showed that the hot tearing of the alloy is due to dendrite separation caused by the solid phase shrinkage could not be filled with intergranular residual liquid phase,or crack propagation could not be effectively suppressed at the end of solidification.With the increase of Mg/Si ratio,the intergranular residual liquid phase increased at the end of solidification,the latent heat released from Mg₂Si phase increased and the pinning effect on grain boundary increased,thus reduced the hot tearing susceptibility of Al-xMg-1Si alloys.With the increase of Mg/Si ratio,the intergranular residual liquid phase increased at first and then decreased at the end of solidification,the latent heat released from Mg₂Si phase increased at first and then decreased,and the pinning effect on grain boundary of Al-3（Mg+Si）alloys increased at first and then decreased,thus the hot tearing susceptibility of the alloys decreased at first and then increased.