Li Wen-xian

Mechanical properties and microstructure of as-cast and extruded Mg-(Ce, Nd)-Zn-Zr alloys ®

Studies on the mechanical properties and microstructures of as-cast and extruded Mg-Ce-Zn-Zr and Mg-Nd-Zn-Zr alloys have been made before and after heat treatment. The results show that the mechanical properties of as-cast Mg-Ce and Mg-Nd alloys are as good as those of typical die cast AZ91 alloy and the heat resistant WE43 alloy. In Nd-containing alloys, the precipitated phase Mg12 Nd contributes significantly to age hardening. The mechanical properties of extruded alloys are improved obviously compared with those of as-cast alloys. The ultimate strength is 257.8 MPa for extruded Mg-Ce alloy and 265.6 MPa for extruded Mg-Nd alloy. Extrusion is a useful method to improve both the strengths and elongations of the two experimental alloys at both ambient and elevated temperatures. The grain refinement and precipitation strengthening are the main strengthening mechanisms in the alloys. Tensile fracture surfaces show a dimple pattern after extruding and therefore reflect an improved elongation.

Devitrification behaviour of rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy prepared by melt spinning method

Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry (XRD) and high resolution transmission electron microscopy (HRTEM). The results show that, the whole devitrification of rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, EIso and EKis and growth activation energies Eg are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the α(Al) particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α(Al) particles. For secondary crystallization, EIso, EKis and Eg of the first reaction are about 291, 208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.

Second phases of rapidly solidified AlFeCrZrVSi alloy and their thermal stabilities

The rapidly solidified powder of AlFeCrZrVSi aluminum alloy was prepared using multi-stage atomization and consolidated by hot-extrusion, the evolution of microstructure of the extruded materials during thermal exposure was studied with optical microscope, X-ray diffraction and transmission electron microscope (TEM). The results show that the majority of dispersions present in the as-extruded alloy are metastable Al12 (Fe, Cr, V)3Si, which has excellent thermal-dynamical stability and coarsening resistance; the coarsening rate-controlling process of the Al12 (Fe, Cr, V)3Si phase is considered to be diffusion of Fe atom along grain boundaries instead of bulk diffusion of Fe atom.

Heat Treatment of Spray Deposition SiCp/6066 Aluminum Matrix Composites

Heat treatment of spray deposition 10% SiCp/6066 (ϕ(SiCp) = 10%) composites was investigated by means of hardness measurement. The results show that heat treatment technology is influenced by the presence of SiC particles. Compared with the base alloy 6066, the composites have lower burning temperature and is burnt at 540 °C due to the enrichment of Mg and Cu atoms in the SiCp/6066 interfaces. As a result, solution treatment of the composites should be carried out at lower temperature. The aging parameter values such as the aging temperature, the precipitation temperature of β′ and β phases, as well as the peak aging time, become lower. The optimum heat treatment process conditions are that the composites are solution-treated at 515 °C and aged at 165 °C for 5 h.