Study On Technology And Properties Of Al₂O_3f/AZ91D Composite Prepared By Pressrueless Infiltration Method

In the paper,Al₂O_3f/AZ91D composite was prepared by using the method of Pressureless Infiltration process,Its microstructure,mechanical properties,friction and wear behaviour were studied by Optical microscope,SEM,XRD and EDS.Large numbers of micro-porosities in the preform made after optimizing the process could be seen in the SEM picture.Porosity of the preform was more than 72%,and it increased with increasing mass fraction of carbon powder.When mass fraction of carbon powder was less than 20wt.%,Porosity changed evidently with increasing in the mass fraction.In contrast,when mass fraction of carbon powder was more than 20wt.%,the change extent of Porosity became flat.It was discovered that infiltration and forming in the experiment could be accomplished as holding temperature higher than 635℃and holding time longer than 40min.Besides Al₂O₃ fiber with long-rod and spotty shape and Mg matrix,a small quantity of micro porosity and Mg₂Si phase could be seen in microstructure of the composite also.With increasing in holding temperature or holding time,the amount of micro porosity decreased while the amount and dimension of Mg₂Si phase increased which impact hardness of the composite evidently.Al₂O₃ fiber and Mg matrix combined well at the interface where Mg₂Si exist nearby.A layer film with deeper color on the surface of Ao₂O₃ fiber was judged for MgO by EDS analysis.With increasing of Al₂O₃ fiber content,hardness of composite present a up-trend and was greater than AZ91D magnesium alloy.Change trend of the hardness rose gently with increasing of holding time,while it declined gently after increased with increasing of holding temperature.Critical load from slight wear to severe wear was found in friction and wear experiment. With increasing of Al₂O₃ fiber volume fraction,the critical transformation load increased.A critical value about the wear rate of composite which was affected by Al₂O₃ fiber content existed,it appeared when the volume fraction of Al₂O₃ fiber was 18 vol.%.With applied loads increasing,the wear mechanism changed from low stress abrasion and slight adhesive wear to severe high temperature adhesive wear.With fiber volume fraction increasing,the wear mechanism of composite changed from adhesive wear to low stress abrasion and slight adhesive wear.When fiber volume fraction was 18vol.%,the critical transform temperature from slight wear to severe wear of composite was 250℃.During low temperature period,the abrasion wear took as the dominant and the slight adhesive wear as the subsidiary.With increasing the temperature adhesive wear became severe and finally turned to high temperature severe adhesive wear.