An Investigation on Microstructure Evolution, Mechanical Properties, and Strain Aging of Mg-1.8Zn-0.7Si-0.4Ca Biomedical Alloy Processed by Equal Channel Angular Pressing

摘要

The influence of equal channel angular pressing (ECAP) on microstructure and mechanical behavior, as well as, strain aging during ECAP and post-ECAP of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy was examined. The alloy in solid solution heat-treated condition was processed by ECAP with route B-C at 350 and 400 degrees C. The specimens ECAPed at 350 degrees C were aged at 125 and 150 degrees C for different times. The hardness and shear punch test results indicated that performing ECAP at 350 degrees C for 4 passes increases the hardness and shear strength of the alloy from 48 HV and 110 MPa to 71 HV and 188 MPa, respectively. It was revealed that the average grain size of the alloy decreases from 78 mu m to about 3 mu m after 4 passes of ECAP. Three precipitates of CaMgSi, Ca2Mg6Zn3, and Mg2Si were detected in the solid solution specimen. After 4 passes of ECAP at 350 degrees C, Ca2Mg6Zn3 was completely dissolved and the morphology of Mg2Si changed from Chinese script to fiber-shaped particles. Dynamic strain aging occurred at high-temperature ECAP, and the specimens were overaged during post-ECAP aging. Small MgZn particles were detected in the overaged sample.