Study On The Surface Layer Properties Of Aluminium Alloy 6061 Based On Rotary Ultrasonic Assisted Rolling Process

Aluminium metal mirrors are widely used in space astronomy due to their light weight and good reflectivity.In the process of metal reflector processing,due to the low surface hardness and coarse surface grain of aluminum alloy material,there are phenomena such as sticky tool during processing,resulting in poor surface quality to meet the optical performance requirements of reflector.Therefore,in this paper,the surface of aluminum alloy 6061 material is strengthened by using rotary ultrasonic rolling process.The combination of roll processing and ultrasound-assisted method enables the surface to undergo strong plastic deformation and form a fine grain layer to improve the mechanical properties of the surface layer while maintaining the original state of the material matrix.In order to prepare the surface of high performance aluminum alloy 6061 material and to investigate the relationship between the surface quality of aluminum alloy 6061 material and the rotary ultrasonic rolling process,the main research contents and results of this paper are as follows.(1)A planar multi-roller type roll machining tool was designed considering the roller contact method and machining efficiency.The contact method used in this tool is linear contact,which can effectively increase the contact area between the roller and the workpiece surface during the rotary rolling process and improve its processing efficiency.(2)Analysis of the effects of different machining parameters on roughness,hardness and grain size based on orthogonal experiments.The experimental group parameters of optimal material surface roughness,surface hardness,and surface grain size are obtained by calculating the polar differences.Optimal roughness process parameters:?=1000rpm,V_c=40mm/min,F=600N,n=2.Optimal hardness process parameters:?=2500rpm,V_c=80mm/min,F=800N,n=4.Optimal grain size process parameters:?=1500rpm,V_c=40mm/min,F=400N,n=1.(3)The experiments of rotary ultrasonic rolling processing were carried out to analyze the effects of processing parameters on surface morphology,roughness and grain size.Experimental results show that the increase in the number of rolls during the rotary ultrasonic rolling process causes the roughness value to decrease and then increase.An increase in the applied pressure causes a decrease and then an increase in the roughness value.An increase in the lateral feed rate of the rolling head causes the roughness value to decrease,then increase and then decrease.The increase in spindle speed causes a gradual increase in roughness values.The increase in the number of rolling without ultrasonic assistance will cause the roughness value to increase gradually;the increase in the applied pressure value will cause the roughness value to increase and then decrease;the increase in the transverse rate will cause the roughness to decrease gradually;the increase in the machine spindle rotation speed will cause the roughness to become smaller and then larger.The grain size of the non-sonic tumbling processed surface ranged from35-48 nm,with a grain size reduction of 14-27 nm.(4)The experiments of rotary ultrasonic rolling processing were carried out to analyze the effects of parameters on hardness,elastic modulus and residual stress during the experiments.The experimental results show that:the surface hardness of the material tends to level off with the increase of rolling times,and the hardness increases by 19-22.9%compared with that before rolling;it increases first and then decreases with the increase of static pressure,and the hardness increases by 12-21%compared with that before rolling;when the transverse rate increases,it causes the hardness to become smaller and then larger,and the hardness increases by 21-23%compared with that before rolling;it increases first and then decreases with the increase of spindle speed,and the hardness increases by 16.5-22%compared with that before rolling.increase 16.5-22%.When the number of rolling increases the modulus of elasticity value will slowly become smaller,its reduction rate is not obvious,compared with the pre-rolling modulus increased by 13.3-18.83%;when increasing the surface fixed pressure the modulus of elasticity first becomes larger and then becomes smaller,compared with the pre-rolling modulus of elasticity increased by 3.43-18.83%.The stress within the surface tissue changes from tensile stress to compressive stress after this method of processing.When the number of reciprocation is continuously increased the stress also becomes larger,the maximum value is-724MPa,and the maximum stress layer is about 0.65mm;when the value of fixed pressure on the surface is increased the stress also becomes larger,the maximum stress is-752MPa,and the maximum stress layer is about 0.8mm.