Study On WE43/nHA Composite Prepared By Friction Stir Processing

Mg-RE alloys have a series of advantages such as excellent strength at room temperature,good biocompatibility,degradable in physiological environment and the degradation products were proved harmless.Therefore,Mg-RE alloys have certain application prospects in the field of biomedical materials.However,the poor plastic deformation ability at room temperature and excessively rapid corrosion rates in Cl~-containing environments of Mg-RE alloys limit their application in the field of biomedical materials.Introducing hydroxyapatite(HA)particles into the magnesium alloy matrix is an effective way to improve the corrosion resistance and biocompatibility of magnesium alloys.Friction stir processing(FSP)is a novel severe plastic deformation processing technology for preparing fine-grained materials with good comprehensive mechanical properties.Therefore,in this study,the as-cast WE43 Mg-RE alloy was used as the base metal(BM),and the nano-hydroxyapatite(nHA)particles were used as the reinforcing phase,two passes of FSP were performed to prepare WE43/nHA composite.The effects of process parameters on the microstructure,mechanical properties and corrosion behavior of WE43/nHA composites were studied.This research aims to provide technical reference and experimental basis for the preparation of HA reinforced magnesium based composites by FSP technology.Firstly,two passes of FSP were conducted on the as-cast WE43 magnesium alloys with a traverse speed of 60 mm/min and rotating speed of 1000 r/min and 1400 r/min,respectively.The microstructure evolution and mechanical properties of FSP-WE43 specimens prepared under the combination of two processing parameters were investigated.After two passes of FSP,the grain size of the as-cast WE43 magnesium alloy was remarkably refined,and the mechanical properties were significantly improved.The microstructure and mechanical properties of the specimens prepared at the rotating speed of 1000 r/min and 1400 r/min were similar with each other.With the increase of rotating speed,the heat input in stir zone increased and the average grain size increased slightly.Secondly,the as-cast WE43 magnesium alloy was used as the base metal,nHA particles were used as the reinforcing phase,and two passes of FSP were performed to prepare WE43/nHA composite.The rotating speeds of 600 r/min,1000 r/min and 1400 r/min were selected and the traverse speed was fixed at 60 mm/min.The microstructure evolution and mechanical properties of WE43/nHA composites prepared under different processing parameters were studied.The distribution of HA particles in the composite is mainly affected by the rotating speed of the FSP tool.At lower rotating speed,HA particles are prone to agglomerate locally,resulting in non-uniform microstructure.As the rotating speed increased up to 1000 r/min,HA particles dispersed uniformly in magnesium matrix.Compared with the FSP-WE43 specimen without addition of HA particles,the grains in stir zone of WE43/nHA specimen was further refined owing to the pinning effect of HA particles.The addition of HA particles also increased the microhardness of as-cast WE43 magnesium alloy,but locally agglomerated HA particles slightly reduced the strength and ductility.In general,the agglomeration phenomenon was not serious,thus the strength and elongation of the WE43/nHA specimen were still significantly improved compared with the base metal.Finally,the corrosion behavior of BM and FSP-WE43 and WE43/nHA specimens in simulated body fluids(SBF)was studied.In the same immersion period,the BM specimen exhibited poor corrosion resistance,severe corrosion occurred and a large amount of material peeled off.Due to the grain refinement and the broken of coarse second phases caused by FSP,the corrosion resistance of FSP-WE43 specimen was greatly improved.With the addition of HA particles,corrosion resistance of the material was further improved,WE43/nHA specimen exhibited the characteristics of uniform corrosion,which was required for biomedical materials.The mechanical properties test results after immersion showed that after immersion for 72 hours,the maximum tensile load of the BM specimen was only 14%of the initial value,indicating that the bearing capacity was lost.The maximum tensile load of the FSP-WE43 and WE43/nHA specimens were 69%and 70%of the initial value respectively,which means a certain load-bearing capacity of those specimens was retained after immersion for 72 hours.