Effect Of Heat Treatment And Processing On The Tissue Properties Of CaO/AZ91 Composites

Mg is currently the lightest metal material,its specific strength,specific stiffness,excellent shock absorption performance,fluidity,dimensional stability and resistance to electromagnetic interference,therefore,in the aerospace,automotive,marine,3C and other fields are widely used.However,magnesium alloys have disadvantages such as low plasticity,processing difficulties and casting defects,and poor corrosion resistance,and their use is somewhat limited.In this study,commercial AZ91 alloy and CaO/AZ91 composites were studied,and the materials were die-cast,heat-treated and extruded to investigate the effects of different processing and treatment processes on the tissue properties of AZ91 alloy and CaO/AZ91 composites,and to investigate the possibility of the application of extruded AZ91 alloy and CaO/AZ91 composites in the field of biomedical materials.A preliminary exploration was carried out,and the experimental results obtained are as follows.(1)The addition of CaO particles to the die-cast CaO/AZ91 composite transforms the second phase from a continuous coarse mesh structure to a discontinuously distributed fine diffuse intermetallic compound Mg-Al-Zn-Ca phase,resulting in Vickers hardness,ultimate tensile strength and yield strength of CaO/AZ91 composite of 110 HV,223 MPa and 137 MPa.The corrosion resistance is better than that of AZ91 alloy in die-cast state.(2)The mean grain size of CaO/AZ91-T4 was the smallest and the mechanical properties were the best at 420 ℃×8 h.The as-cast material obtained by gravity casting was subjected to solid solution treatment for different times.The Vickers hardness of CaO/AZ91-T6 was the highest(120 HV)at 12 h.Therefore,the aging process was selected as 170 ℃×12 h.The hardness of CaO/AZ91-T6 was the highest at 12 h.(3)The extruded material undergoes dynamic recrystallization and precipitates fine Mg17Al12 and Mg-Al-Zn-Ca phases,among which CaO/AZ91-T6-EX composite has small grain size and fine diffuse distribution of the second phase,with the best mechanical properties,the Vickers hardness value,ultimate compressive strength and yield strength reach 130 HV,555 MPa,346 MPa,and the corrosion state is homogeneous.(4)The pre-aged extruded state material showed non-toxicity in cell experiments and the CaO/AZ91-T6-EX material promoted cell proliferation,and the annual corrosion rate of CaO/AZ91-T6-EX by immersion was 0.486 mm/y.