ORIGINAL ARTICLEProducing of AZ91/SiC composite by friction stirprocessing (FSP)Parviz Asadi&Ghader Faraji&Mohammad K. BesharatiReceived: 7 September 2009 /Accepted: 24 February 2010 /Published online: 10 April 2010#Springer-Verlag London Limited 2010AbstractFrictionstirprocessing(FSP)wasusedtofabricate SiC/AZ91 composite layer. Effect of processparameters such as rotational and traverse speeds, toolpenetration depth and tilt angle on the formation of defectssuch as cracks, tunnelling cavity and also on sticking ofmatrix material to the tool was investigated. Also, effect ofthese parameters was studied on the mechanical propertiesand microstructures of specimens. Microstructure studieswere carried out by optical and SEM. Results showed thatFSP is an effective process to fabricate SiC/AZ91 compos-ite layer with uniform distribution of SiC particles, goodinterfacial integrity and significant grain refinement. In-creasing the rotational speed leads to a decrease in the grainsize and an increase in the traverse speed leads to adecrease in the grain size. There are upper and lowerlimitations for these speeds which were determined. PD is amore effective parameter to produce sound surface layer.PD value was affected by traverse and rotational speeds andthe tilt angle values. This study shows that by using 5μmSiC particles, the stir zone grain size reduces from 150 to7.17μm and stir zone hardness increases from 63 to 96 Hv.KeywordsAZ91.Particulate.FSP.Microstructure.Microhardness.Composite1 IntroductionAbilityofmagnesium-basedalloystoexhibithighermechanical properties and offer significant weight savingshas fuelled research activities recently [1]. Magnesium isthe lightest constructional metal on the Earth; it is 35%lighter than aluminium and 78% lighter than steel [2,3].Hence, applications stretch from aerospace and automobileindustries in replacing aluminium and steel to electronicand computer industries replacing plastics [1]. However,the mechanical properties, such as the hardness of themagnesium alloys, are not sufficient to enhance theirapplications, though some processes to fabricate ceramicsparticles/magnesium alloy composites have been studied toimprove the mechanical properties [1-9].Recently, FSP has been developed based on friction stirwelding for microstructure modification of the metals. It ispossible to produce surface composite layer by this processas well. Hsu et al. [10] produced Al–Al3Ti nanocompositelayer by FSP and improved the Young modulus and thetensilestrengthofaluminium.TheyshowedthattheYoung’s modulus of the Al–Al3Ti composite increasessignificantly with increasing the volume fraction of Al3Ti inthe matrix. By addition of 15% Ti, the Young modulus canreach 114 GPa, which is 63% higher than that of Al. Aboutthe magnesium, much attention has been paid to increasethe mechanical properties of AZ31 magnesium alloy byFSP.Darrasetal.[3]usedFSPformodifyingthemicrostructure and the mechanical properties of AZ31B-H24 magnesium alloy. Woo et al. [4] investigated themicrostructure, hardness, tensile behaviour and residualstressesofAZ31Bmagnesiumalloyinfrictionstirprocessing. Morisada et al. [2,5] and Chang et al. [6,7]similarly investigated the microstructure, and the mechan-ical properties of friction stir processed (FSPed) AZ31magnesium. However, friction stir processing of AZ91magnesium alloy is difficult, because of its weak formabil-
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