Study On The Evolution Behavior Of Surface Morphology Of 6061 Aluminum Alloy Laser Cleaning And Optimization Of Process Parameters

Aluminum alloy has the advantages of low density and high specific strength.It is widely used as the car body material.However,its surface oxide layer will affect the welding quality.So a high-quality and efficient removal technology is urgently needed.Laser cleaning is a process that uses pulsed laser to remove surface substances.It has the advantages of non-contact and good controllability.The surface morphology changes caused in the laser cleaning process will affect the subsequent processing such as welding and coating.At present,there are few studies on the evolution behavior of aluminum alloy surface morphology.And the formation mechanism of the morphology is still unclear.In this paper,the surface morphology changes during the laser cleaning process are studied.First,based on the process experiment method,the relationship between the laser cleaning process parameters,surface morphology and roughness was explored.Then,the model of the aluminum alloy laser cleaning was established to analyze the evolution behavior of the surface morphology.Finally,the response surface optimization method was used to optimize the laser cleaning process parameters to obtain the best surface morphology.The results obtained are as follows:(1)The correlation among process parameters,surface morphology and roughness was explored.The laser cleaning process window for the natural oxide layer on 6061aluminum alloy was established.It was found that:(a).With the increase of power(P),the roughness shows an increasing trend.When the laser power increases from 15 W to 75 W,the roughness increases from Sa 0.608?m to Sa 1.636?m.(b).As the scanning speed(v)and line spacing(l_y)increasing,the roughness first increases and then decreases.When the laser power is 45 W,the roughness reaches the maximum that is Sa 1.364?m at the position where the scanning speed is 4000 mm/s and the line spacing is 0.04 mm.(c).The laser cleaning process window for the natural oxide layer on 6061 aluminum alloy is:30W?P?60 W,3000 mm/s?v?5000 mm/s,0.03 mm?l_y?0.05 mm.(2)The heat transfer and flow coupling model of 6061 aluminum alloy laser cleaning was established.The evolution behavior of surface morphology during laser cleaning was analyzed.It was found that:(a).In the process of laser cleaning with low power(20W),the1?m-thick material layer reaches the vaporization temperature.The surface morphology changes smoothly.The fluid on the middle of the molten pool flows to the deep,refluxing near the solid-liquid interface.The maximum flow velocity is 5 m/s,forming a small crater.There is no metal splash.The height of surface topography is 2?m.(b).During the laser cleaning process with high-power(40 W,60 W),there are 3?m-thick and 6?m-thick material layers reaching the vaporization temperature.Maximum flow speed is 150m/s.The melt flying off the surface leads to the formation of larger craters.The heights of surface topography are 7?m and 17?m.(c).The depth of the molten pool reaches 4.5?m,5?m and 8?m when the laser power is 20 W,40 W and 60 W,respectively.The splashed droplets take away a lot of heat.During the cleaning process with the laser power of 60 W,the surface temperature has dropped below the solidus temperature at 0.6?s.(3)Based on the laser cleaning process window established above,a response surface model of the relationship between process parameters and roughness was constructed.The process parameters were optimized with the goal of maximizing the roughness.It was found that:(a).Within the parameter range of 30 W?P?60 W,3000 mm/s?v?5000mm/s and 0.03 mm?l_y?0.05 mm,the order of significance of the effect on roughness is:average power,scanning speed,line spacing.(b).The process parameters that reach the maximum roughness within this process parameter range are that laser power is 60 W,scanning speed is 4950 mm/s and line spacing is 0.041 mm.And the surface roughness is Sa 1.584?m.According to the test results of elemental energy spectrum,the relative content of oxygen on the surface after laser cleaning is less than 1%,which meets the needs of industrial applications.