สมบัติการคืบของโลหะสังกะสีผสม ZA-27 ที่หล่อขึ้นรูปโดยวิธีการหล่ออัดสเลอร์รี

Abstract

The purpose of this research was to study creep property of ZA-27 zinc alloy prepared by conventional squeeze casting (CSC) and slurry squeeze casting in which the semi-solid molten alloy was made by the GISS technique. In the study, three groups of specimens were prepared, including the conventional squeeze casting (CSC), the slurry squeeze casting using the GISS time for 5 seconds (GSC5s) and the slurry squeeze casting using the GISS time for 15 second (GSC15s). Before mechanical tests the specimens were heat treated by homogenization at 320°C for 3 hours and artificial ageing at 100°C for 1 hour. The mechanical tests consisted of tensile tests and creep tests at temperatures of 25, 100 and 140°C. The results showed that the CSC had higher tensile strength than the GSC5s and GSC15s, however it had lower ductility than the other two. Because the CSC was composed of dendritic structures of Al-rich α phase which was more resistant to tensile stress than the GSC5s and GSC15s which were globular structure. The results of creep tests showed that at 25, 100 and 140°C the CSC had higher creep resistant than the GSC5s and GSC15s. The stress exponent, n of the three groups of specimens tested in the stress range of 80- 140 MPa was about 3.4-5.1 The value of n indicated that creep might be controlled by the dislocation glide-climb mechanism. However, in the low stress range of 20-80 MPa, at 140°C creep might be controlled by the diffusional creep mechanism, where n was about 1-2. In addition, it was found that in the stress range of 80-140 MPa and the temperature range of 25-140°C, the averaged activation energy for creep, Qc of CSC, GSC5s and GSC15s were 33.7, 28.4 and 18.2 KJ/mol, respectively.