Research On Forming Mechanism And Wear Performance Of Al Based Composites Manufactured By Selective Laser Melting

The advanced selective laser melting?SLM?technology was employed to prepare Al based composites.It turned out that Al₂O₃/Al and in-situ Al₂Si₄O₁₀/Al composites were successfully fabricated by SLM of Al₂O₃/Al and Al₂O₃/Al Si10 Mg composite powders.The influence of laser process parameters on the phase constituent,densification behaviour,microstructural characteristics,microhardness and wear property of SLM-manufactured AMCs samples was studied.An in-depth relationship among SLM processing conditions,microstructural characteristics and mechanical performance of the composite parts was well developed,in order to optimize the laser process parameters,as well as obtain desirable parts with unique microstructural features and mechanical performances.Besides,the friction and wear properties of the optimally prepared Al₂Si₄O₁₀ reinforced Al matrix composites were evaluated on a ball-on-disk tribometer by rubbing against stainless steel at room temperature.The major conclusions could be drawn as follows:In the SLM processing of Al₂O₃/Al composite parts,when the applied ? is low,the Al₂O₃ reinforcing phase presenting a fragmentized feature seriously aggregated into large block clusters in the Al matrix,simultaneously establishing a poor particles/matrix interface with obvious interfacial defects.Moreover,the cross section consisted of large metallurgy defects and the corresponding densification rate was relatively low.These behaviors considerably lowered the mechanical performance of the composite part.A reasonable increase of ? to 236 J/m resulted in the presence of a pretty dense cross section with a considerably high density of 97.3% TD.A large amount of fine long-strip Al₂O₃ reinforcements uniformly dispersed along the boundaries of melt pool.Moreover,a clean and compatible matrix/particles interface was generated.In this instance,the Al₂O₃/Al composite part demonstrated the superior hardness with a high average of 175 HV0.1 as well as excellent wear property with a considerably low,steady value of 0.11 and a significantly reduced wear rate of 4.75×10-5 mm3 N-1 m-1.In the SLM processing of in-situ Al₂Si₄O₁₀/Al composite parts,both the fragmentized Al₂Si₄O₁₀ reinforcements with poor bonding and integrity at a low n of 200 J/m and the severely coarse grain at a high n of 350 J/m lowered the performance of the composite parts.At the optimal n of 289 J/m,the desirable microstructures with the novel,refined and well-bonded ring-structured Al₂Si₄O₁₀ reinforcements with an average thickness of 0.3 ?m distributing homogeneously along the grain boundaries of the cellular dendritic Al matrix could be tailored in the track core.Simultaneously,in the track overlap,the slightly coarse ring-structured Al₂Si₄O₁₀ reinforcements with an average thickness of 0.38 ?m and large amounts of dispersive Al₂Si₄O₁₀ particle reinforcements were observed in the columnar dendritic Al matrix.The performance of SLM produced in-situ Al₂Si₄O₁₀/Al composite part thus showed considerable improvement.In the friction and wear process of SLM prepared in-situ Al₂Si₄O₁₀ reinforced Al matrix composite parts,when the applied load increased,more particles tended to be pulled out,then be broken,hence initating the serious three-body abrasive wear and giving rise to further disruption to the worn surface.With sliding speed going up,more friction heat was accumulated on the worn surface,thus elevating the rate of the formation of Al₂O₃ layer and the transfer of Fe₂O₃ layer,which greatly contributed to the improvement of wear property of the composite part.During the process of long time friction and wear,the COF fluctuated between 0.55 and 0.65.However,in the later stage of wear,the enough frictional heat gathering on the worn surface offered a great drive force for the formation of surface Al oxide,combined with large numbers of the transfer of Fe oxides well explained the reduced fluctuation extent of COF.