Page - 3 - in 3D Printing of Metals

metals Review SelectiveLaserMeltingofMagnesiumand MagnesiumAlloyPowders:AReview VyasarajManakari,GururajParandeandManojGupta* DepartmentofMechanicalEngineering,NationalUniversityofSingapore,9EngineeringDrive1, Singapore117576,Singapore;mbvyasaraj@u.nus.edu(V.M.);gururaj.parande@u.nus.edu(G.P.) * Correspondence:mpegm@nus.edu.sg;Tel.:+65-6516-6358 AcademicEditor:HugoF.Lopez Received: 9September2016;Accepted: 15December2016;Published: 26December2016 Abstract:Magnesium-basedmaterialsareusedprimarily indevelopinglightweightstructuresowing to their lowerdensity. Further, beingbiocompatible theyofferpotential foruse as bioresorbable materials fordegradablebonereplacement implants. Thedesignandmanufactureofcomplexshaped componentsmadeofmagnesiumwithgoodqualityare inhighdemandintheautomotive,aerospace, andbiomedicalareas. Selective lasermelting(SLM) isbecomingapowerfuladditivemanufacturing technology,enablingthemanufactureofcustomized,complexmetallicdesigns. Thisarticle reviews therecentprogress in theSLMofmagnesiumbasedmaterials. EffectsofSLMprocessparameters andpowderpropertiesontheprocessinganddensificationof themagnesiumalloysarediscussed indetail. Themicrostructureandmetallurgicaldefectsencountered in theSLMprocessedpartsare described.ApplicationsofSLMforpotentialbiomedicalapplications inmagnesiumalloysarealso addressed. Finally, thepapersummarizes thefindings fromthis reviewtogetherwithsomeproposed futurechallenges foradvancingtheknowledge in theSLMprocessingofmagnesiumalloypowders. Keywords: selective lasermelting (SLM);magnesium; additivemanufacturing; microstructure; mechanicalproperties; corrosionbehavior 1. Introduction Magnesium (Mg) is the sixthmost abundant element in the earth’s crust comprising about 2.7%of its composition [1].Magnesiumbasedmaterialsarepreferredwhentargetingweight-sensitive applications, as theyare the lightest structuralmaterial availablewith adensity of only 1.74g/cc which is~33%,~61%and~77%lower than thatof aluminium, titanium,and iron, respectively [2]. Increasing demand for light weighting drives the interest formagnesium to be used in various engineering applications to achieve higher fuel economy, emission reduction etc. Other than its lowdensity,magnesiumbasedmaterialsalsoexhibithighspecificmechanicalproperties, excellent castabilityandmachinability,highdampingcharacteristics,highthermalstability,highthermaland electrical conductivity, andresistance toelectromagnetic radiation [3–7]. However, theapplication areasofmagnesiumhavebeen limitedbyits lowcorrosionresistanceandrelativelypoormechanical properties, such as low elastic modulus, low strength, limited room temperature ductility and toughness, rapid lossofstrengthwith temperature,andpoorcreepresistance [8,9]. Even thoughmagnesiumbasedmaterials arenot suitablewhere ahighmodulus is required, a rangeofapplicationshasbeenevaluated in thebiomaterialsarea in therecentpast. Thecombination ofsuperiorbiocompatibility,biodegradability, elasticmoduluscloser tohumanbone,andfavourable mechanical propertiesmakesmagnesiumone of themost sought aftermaterials for orthopaedic applications like implants and fixation devices [10]. In the recent past, manymagnesiumalloys havebeendeveloped targetingbiomedical applications ranging frommaxillofacial reconstruction, to paediatric orthopaedics, vascular stents, surgical clips, screws, plates, and bone-interfacing Metals 2017,7, 2 3 www.mdpi.com/journal/metals