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metals Article Effectof theThermodynamicBehaviorofSelective LaserMeltingontheFormationofInsituOxide Dispersion-Strengthened Aluminum-BasedComposites LianfengWang1,4,5, JiubinJue2,3,MujianXia2,3,LijieGuo1,5,BiaoYan4andDongdongGu2,3,* 1 ShanghaiAerospaceEquipmentsManufacturer,Shanghai200245,China;wlf149@163.com(L.W.); guolijie149@163.com(L.G.) 2 CollegeofMaterialsScienceandTechnology,NanjingUniversityofAeronauticsandAstronautics, YudaoStreet29,Nanjing210016,China; jiubinjue@hotmail.com(J.J.); xmjnuaa@nuaa.edu.cn(M.X.) 3 InstituteofAdditiveManufacturing(3DPrinting),NanjingUniversityofAeronauticsandAstronautics, YudaoStreet29,Nanjing210016,China 4 MaterialScienceandEngineeringDepartment,TongjiUniversity,Shanghai200092,China; 84016@tongji.edu.cn 5 ShanghaiResearchCenterofComplexMetalPartsbyAdditiveManufacturing,Shanghai200245,China * Correspondence: dongdonggu@nuaa.edu.cn;Tel.:+86-25-5211-2626 AcademicEditor:ManojGupta Received: 18 July2016;Accepted: 9November2016;Published: 19November2016 Abstract: This paper presents a comprehensive investigation of the phase and microstructure, the thermodynamic behavior within the molten pool, and the growth mechanism of in situ oxidedispersion-strengthened (ODS) aluminum-basedcompositesprocessedbya selective laser melting (SLM)additivemanufacturing/3Dprintingprocess. Thephaseandmicrostructurewere characterized byX-raydiffraction (XRD) and a scanning electronicmicroscope (SEM) equipped with EDX, respectively. The thermodynamic behaviorwithin themolten poolwas investigated for a comprehensiveunderstandingon the growthmechanismof the SLM-processed composite usingafinitevolumemethod(FVM).Theresults revealedthat the insituAl2Si4O10ODSAl-based composites were successfully fabricated by SLM. Combined with the XRD spectrum and EDX analysis, the new silica-rich Al2Si4O10 reinforcing phase was identified, which was dispersed around the grain boundaries of the aluminummatrix under a reasonable laser power of200W. Combined with the activity of Marangoni convection and repulsion forces, the characteristic microstructureofSLM-processedAl2Si4O10ODSAl-basedcomposites tendedto transfer fromthe irregularnetworkstructure to thenearlysphere-likenetworkstructure inregular formbyincreasing the laserpower. Theformationmechanismof themicrostructureofSLM-processedAl2Si4O10ODS Al-basedcomposites is thoroughlydiscussedherein. Keywords:selectivelasermelting;aluminummatrixcomposites;microstructure;thermodynamicbehavior; formationmechanism 1. Introduction Aluminummatrixcomposites (AMCs)havebeenwidelyused inmanyapplications, especially in the aerospace, defense, andautomobile industries, due to its unique combinationof lightweight, highspecificstrength,andexcellentwearperformance[1].Nevertheless, the limitedwearresistance andothermechanical properties becomea serious barrier for the applicationwhere abrasive and erosion phenomena exist. Thus, a considerable number of previous efforts have been attempted Metals 2016,6, 286 108 www.mdpi.com/journal/metals