Calcium-magnesium Alloy AM40 Low Microstructure And Mechanical Properties

In recent years,due to the emphasis on material light design,reducingenergy consumption and growing of environmental awareness,lightweightmaterials have been paid more and more attention.Magnesium alloys aregradually replacing of aluminum alloys and plastic products become idealsubstitute materials in the high-technology fields and civil producingindustries.Alkaline earth elements are one of the vigorous alloying elements ofmagnesium alloys,such as Ca、Sr,etc.These elements are not only much cheaperthan the price of rare earth elements,but also can refine the microstructure of thealloy,enhance its tensile strength and yield strength.Therefore,broaden appliedrange of magnesium alloys in the case of low-cost situation.In this dissertation,the Mg-Al alloy system was chosen as researchobject,and processed by hot extrusion after homogenizing annealing in the caseof different contents of Ca.Then solution treatment and aging treatment ofdifferent time after extrusion.The influences of different contents of Ca on themicrostructure and mechanical properties of AM40(Mg-3.5Al-0.5Mn-0.4Sr) alloyin as-cast and heat processed were systematically investigated.The effects ofalkaline elements Ca additions on the microstructure and mechanical propertiesof as-cast and squeeze AM40magnesium alloy were investigated by usingmetallographic microscope(OM),X-ray diffraction(XRD),scanning electronmicroscopy(SEM),Spectrum analysis(EDS),Stretching machine,Hardnesstester,etc.Exploring the effect of solution treatment and aging treatment onextruded magnesium alloy AM40microstructure and mechanical properties.Results of the study as follows:(1) When the calcium content increased from0.5%to0.5%,AM40alloyas-cast organization is the trend of progressive elaboration,mesh of beta phasehas been broken,appeared in the grain boundary and crystals inside a smallamount of granular phase.When adding the1.5%Ca,α-Mg phase is the mostuniform and fine,continuous mesh structure of β-Mg17Al12basicdisappeared,granular phase diffused distribution on the alpha Mg matrix and along the grain boundary appear Al2Ca facies of thermal stability.And after theextrusion organization obviously refinement and uniform distribution.(2) With the increase of Ca content,Mg-Ca and Al-Ca mixing enthalpiesbetween the two constituent element goes negative and the affinity of constituentelement increases,improved second-phase,the grain size of as-cast alloydecreases.(3) Alloy through homogenization annealing and extrusion,a fuller dynamicrecrystallization occurred,forming a number of isometric crystals,grain sizeranging from5um to20um,and10um size more frequently seen.As the calciumcontent increases,isometric Crystal microstructure more finer,Ca solution in theβ-Mg17Al12phase,improves the stability of β-phase,undissolved particles of thegrain boundary increased.(4) Alloy after solid solution and aging treatment,precipitate outsecond-phase that was rod shaped and particles shaped by uniformly distributesin the common role of interfacial energy and strain energy.With Ca contentincreased, the number of spherical particles precipitated increase;Meanwhile,thefigure of vickers hardness has larger improve than cast value,and as Ca contentof increased,the hardness value tendency of alloy first increased and thendecreased.When Ca content reached1.5%and limitation of42h,alloy hardnessfigure reached a peak, and yield strength and tensile strength can reach morethan240MPa and300MPa.(5) Under the common role of Ca elements and extrusion,obviously thegrain became more refinement and improve the second-phase,AM40alloywhich has Ca content of1.5%,yield strength reached279MPa after agingtreatment,tensile strength reached330MPa,elongation reached18.1%.Consequently,has a good development and application value.