Research On The Silicification Of Surface Of Aluminum Alloy

Aluminum alloy has many potential industrial applications owing to its light proportion,high specific strength, good electric and thermal conductivity. With the rapid development ofmodern industry, its low hardness and bad wear-resisting performance etc.in shortcomings insome extent restricted its application. Therefore, the strengthen mothod of the aluminum alloy’ssurface properties has become an important research topic in surface engineering.Among thevarious surface modification treatments of Aluminum alloy, high hardness and excellent wearresistance of high silicon Aluminum alloy attract people’s attention.Laser surface treatmentattracted the attention of many researchers owing to its unique advantages, because lasercladding technique aims at obtaining high perpormance coatings on Aluminum alloy substrates,showing a good application prospect.This paper expounds the preparation of current situation and existing problems of variousproperties of the silicon coating which were cladded on aluminum alloy’ surface, on the basis ofthis and in order to improve the Si aluminum content of the surface of Aluminum alloy.The newmethod of laser assisted silieonizing is raised.Using CO2high-powered laser clad a high Sicoating on the surface of Aluminum alloy,we found laser power and scanning velocity areimportant factors to influence the quality of the cladding, drawing a optimization of processparameters. The cladding layers of macro morphology, microstructure, phase composition, Sicontent, microhardness distribution, friction coefficient in optimizing parameter conditions werecharacterized and analysised. In addition, the laser cladding samples were researched throughheat treatment,drawing a series of experimental datas. It is a new potential technique to producehigh silicon Aluminum alloy.Experiments show that, not reasonable parameters will bring blow hole, crack in the lasercladding layer. The surface of coating has good quality in the optimization parameters （P=2400W, V=300mm/min）. The laser cladding layer could be divided into the cladding zone，theinterface zone and the heat-affected zone along the depth direction. The heat-affected zone is still keeping the original organizations,the microstructures in the interface zone present typicalepitaxy growth;there are a lot of five star、plank primary Si in the cladding zone. The depth ofthe aggrandizement layer could reach1mm above, and Si content of the cladding layer wasobviously higher than the Si content of substrate,Microhardness distribution curve has adownward trend from surface to substrate,the highest hardness can reach to320HV, far higherthan substrate’s. At the same time, the cladding layers’ weight loss was about half of thesubstrate’s, friction coefficient was about0.41,wear resistance increase greatly relative to thealuminum alloy substrate.With the high silicon coating in the optimize laser cladding parameters through differentparameters’ heat treatment,we found that with the extension of heat preservation time and therise of heat temperature, primary Si begins to dissolve and roundness early, but more than acertain of heat time and heating temperature, primary Si begins to worse, appearing to lap jointand grow up,explaining that the shapes of primary Si change through the diffusion of silicon.After calculating the fitting silicon element distribution curve,we know silicon diffusioncoefficient D was4.8942×10^-13m²s^-1、57.6992×10^-13m²s^-1、8.4316×10^-13m²s^-1in450℃、500℃and550℃,diffusion activation energy Q is42.1238×10³J/mol，diffusion constant D₀is5.4089×10-10m²s^-1.At the same time, the hardness is improved greatly, especially distance0.7mm and the deeper area from the surface. The best parameter is36hours’ heat preservationunder500℃, the minimum of the primary Si’s size at this time is about30-32μm;At the sametime, the highest hardness is319HV, the average hardness was increased about7.5%relative towithout heat treatment’;Average friction coefficient is about0.395, it is lower than the substrate’and laser cladding layer without heat treatment （average friction coefficient is about0.41）,showing better hardness and wear-resisting performance.