Effect Of Ca Addition On The Age-hardening Behavior Of Mg-Nd Alloy

Magnesium has been received considerable research for attractive features such aslow density, while its application is limited for few selections and inadquate propertiessuch as yield strength etc..The two strengthening methods including deformationstrengthening and age-hardening are on the basis of precipitates hardening.Therefore,research on precipitates in Mg alloys will present reference for design and production oflow-cost and high-performance Mg alloys.The equilibrium solid solubility of neodymium(Nd) in Mg-matrix is3.65wt pct at552℃and decreased near0at200℃. Neodymium, the low solid solubility rare-elements, is added into Mg matrix in this research inorder to study the effect ofprecipitation evolution on the Mg alloy mechanical properties. It has been confirmedthat calcium enhanced the age-hardening response of Mg alloys and the effect of Cacontent on the binary Mg-2.7wt.%Nd alloy precipitation microstructure and age-hardening response were studied.The conclusion of the research showed that Ca enhanced the age-hardeningresponse of Mg-Nd alloys significantly through solution and aging heat-treatment.Thepeak-aged hardness of Mg-2.7Nd-1Ca was72HV compared with that (60HV) of thebinary alloy and the peak-aged time decreased from1000min to180min in Mg-2.7Nd-1Ca.β—Mg3Nd（a=0.64nm，c=0.52nm）precipitated in the peak-aged binary alloy byTEM and HAADF-STEM and the β had orientation relationships(ORs) with Mgmatrix described as:β1-Mg3Nd （FCC， a=0.74nm） contributed to the strengthening effect inMg-2.7Nd-0.3Ca and the diffraction pattern (DP) showed the precipitation growingalong three variants of1120.Several morphology precipitates precipitated in ternary alloy Mg-2.7Nd-1Caincluding irregular diamond, joint, refined layer section and small amount of chainprecipitates:①the irregular diamond β1-Mg3Nd（FCC，a=0.74nm）growing along three variants of <1120>αcould be obtained by DP;②The joint morphology of precipitates was β1-Mg3Nd and2weight percentcalcium enrichment in the joint section caused two layers lattice distortation;③The phase structure of refined layer section precipitates was not confirmed andit could be the G.P zone prior to the precipitates for the existence of several vacancydefection.④Chain morphology,composed of β1-Mg3Nd and Mg2Ca phase,was studied forthe first time in this research with the enrichment of40weight percent neodymium and7weight percent calcium.