Study On High-Temperature Deformation And High-Cycle Fatigue Properties Of Novel Al-Mg-Si Alloy

In order to achieve the purpose of energy saving and carbon reduction,it is a feasible strategy to use aluminum alloy instead of steel material.However,the strength and fatigue performance of 6XXX series aluminum alloy are still inadequate to meet the actual use demand.Therefore,it is necessary to develop a new Al-Mg-Si alloy with high strength,high toughness and high fatigue resistance with our independent intellectual property rights.In this paper,four new Al-Mg-Si alloys with different Cu contents,namely 0Cu,0.4Cu,0.6Cu and 0.8Cu,were designed and their high-temperature deformation microstructure and high-cycle fatigue properties were studied.The results showed that dynamic recovery is dominant in the hot pressing process while dynamic recrystallization occurs in a small part,and obvious textures are emerged in four alloys after thermocompression.0Cu alloy is dominated by Goss texture with a high proportion of soft orientation texture,while the other three alloys have the equal proportions of Goss,R-Goss and Brass texture with a high proportion of hard orientation texture,which result in the lower strength in 0Cu alloy.The T5 fatigue strength of 0Cu and 0.6Cu alloy is 129.8 and 147.3 MPa,respectively,and the crack propagation mechanisms of them are both along the grain boundary.Owing to the strengthening effect of Cu element on grain boundary,the strength of grain boundary in 0.6Cu alloy is higher and the local deformation at grain boundary become more difficult which leads to the slower propagation rate of crack along grain boundary and the higher fatigue strength.The fatigue strength of T1 and T5 state extruded 0.4Cu alloy is 130.0 and131.7 MPa,respectively,and the crack propagation mechanisms are partly along grain boundary and partly through grain boundary for T5 state and along grain boundary for T1 state.The S-N curve of the 0.4Cu extruded profile has obvious platform due to the competition between crack initiation at the defect and initiation at the residence slip band.Comparing the microstructure and comprehensive properties of the four alloys,due to the low strength in 0Cu alloy and easy overburn while processing in 0.8Cu alloy,meanwhile,0.4Cu and 0.6Cu alloys have good microstructure,mechanical properties and fatigue properties,0.4Cu and0.6Cu alloys are suitable to regard as candidate materials for industrial production.Compared with similar 6061 aluminum alloy on the market,the yield strength,tensile strength,elongation and fatigue strength are increased by 23%,26%,10% and 18%,respectively.