Southwest Technique and Engineering Institute

Chongqing, China

Southwest Technique and Engineering Institute

Chongqing, China
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Cheng Y.-S.,Harbin Institute of Technology | Chen Q.,Southwest Technique and Engineering Institute | Huang Z.-Q.,Harbin Institute of Technology | Huang S.-H.,Southwest Technique and Engineering Institute
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2010

The semi-solid thermal transformation (SSTT) route was used to obtain semi-solid billets for thixoextrusion. Microstructural evolution during partial remelting was studied. Mechanical properties of thixoextruded billets were determined. The results show that the solid grain size decreases initially and then increases as the isothermal holding time increases. Furthermore, shape factor measurements show that the solid grains tend to become increasingly spheroidal after 10 min isothermal holding. With longer isothermal holding time, the degree of spheroidization slightly decreases. Middle ultimate tensile strength (263.3 MPa) is obtained for thixoextruded AZ91D alloy produced by the SSTT route, with a yield strength of 120.0 MPa and an elongation to fracture of 7.19. © 2010 The Nonferrous Metals Society of China.


Zhao Z.,Southwest Technique and Engineering Institute | Chen Q.,Southwest Technique and Engineering Institute | Chao H.,Harbin Institute of Technology | Hu C.,Southwest Technique and Engineering Institute | Huang S.,Southwest Technique and Engineering Institute
Materials and Design | Year: 2011

An as-cast Mg-Al-Y-Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225-400°C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg-Al-Y-Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250°C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg17Al12 was elongated along the extrusion direction. With increasing processing temperature to 350°C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg-Al-Y-Zn alloy. Then billets of as-cast Mg-Al-Y-Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably. © 2010 Elsevier Ltd.


Zhao Z.,Southwest Technique and Engineering Institute | Chen Q.,Southwest Technique and Engineering Institute | Chao H.,Harbin Institute of Technology | Huang S.,Southwest Technique and Engineering Institute
Materials and Design | Year: 2010

Semi-solid processing of magnesium alloys is generally based on conventional magnesium-based casting alloys such as Mg-Al series. However, these casting alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Mg-Zn series. In this paper, a ZK60 magnesium alloy with the addition of Y was thixoforged. The semi-solid thermal transformation (SSTT) route and the recrystallisation and partial melting (RAP) route were used to obtain the semi-solid feedstocks for thixoforging. Microstructural evolution during partial remelting was studied at temperatures for times. Tensile mechanical properties of thixoforged components at room temperature were examined. Results show that a fine spheroidal microstructure can be obtained by the RAP route. Compared to the RAP route, the SSTT alloy shows coarsened solid grains with a relatively high proportion of intragranular liquid droplets. With prolonged holding time, the solid grain sizes of the SSTT alloy and the RAP alloy increased. Coalescence was dominant in the SSTT alloy and Ostwald ripening was dominant in the RAP alloy. Thixoforging for the SSTT alloy and the RAP alloy resulted in successful filling of the die. The tensile properties of the thixoforged RAP alloy were satisfactory and exceeded those of the thixoforged SSTT alloy. However, the mechanical properties of both the thixoforged SSTT alloy and the thixoforged RAP alloy decreased with prolonged holding time. © 2009 Elsevier Ltd. All rights reserved.


Chen Q.,Southwest Technique and Engineering Institute | Huang Z.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Hu C.,Southwest Technique and Engineering Institute
Computational Materials Science | Year: 2013

Thermal stabilities, elastic properties and electronic structures of MgSc, MgY and MgLa have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that MgLa has the strongest alloying ability and structural stability. Gibbs free energy, Debye temperature and heat capacity are calculated and discussed. The elastic constants are calculated, the bulk moduli, shear moduli, Young's moduli, poisson ratio value and elastic anisotropy are derived; the brittleness, plasticity and anisotropy of these phases are discussed. The structural stability mechanism is also explained through the electronic structures of these phases. The ionicity and metallicity of the phases is estimated. © 2011 Elsevier B.V. All rights reserved.


Zhao Z.,Southwest Technique and Engineering Institute | Chen Q.,Southwest Technique and Engineering Institute | Tang Z.,Nanjing University of Aeronautics and Astronautics | Hu C.,Southwest Technique and Engineering Institute
Journal of Alloys and Compounds | Year: 2010

Cyclic closed-die forging (CCDF) was introduced into the strain induced melt activation (SIMA) route to replace conventional upset or extrusion. The microstructure evolution of CCDF formed AM60B magnesium alloy heated into the semi-solid state has been investigated. Tensile mechanical properties for AM60B magnesium alloy thixoformed from starting material produced by the SIMA route were determined. The results show that the SIMA route (four-pass CCDF and partial remelting) produced ideal, fine semi-solid microstructure, in which completely spheroidal primary solid grains had a little amount of entrapped liquid. With increasing the equivalent strain, the solid grain size decreased and the degree of spheroidization tended to be improved. Furthermore, the rate of liquation was also slightly increased. Increasing the reheating temperature was favorable for obtaining spheroidal semi-solid microstructure and decreasing the probability of coalescence among solid grains. However, prolonging holding time resulted in grain coarsening. The tensile mechanical properties of the thixoformed components were influenced by the amount of equivalent strain during CCDF. Good elongation to fracture (15%) was obtained for thixoformed AM60B magnesium alloy component, with a yield strength of 199.2 MPa and a tensile strength of 306.7 MPa. © 2010 Elsevier B.V. All rights reserved.


Chen Q.,Southwest Technique and Engineering Institute | Shu D.,Southwest Technique and Engineering Institute | Hu C.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Yuan B.,Hefei University of Technology
Materials Science and Engineering A | Year: 2012

A multitemperature multi-axial forging (MAF) procedure has been developed to produce a fine-grained AZ61 alloy. The results show that the microstructure can be effectively refined with increasing equivalent strain during MAF. Once dynamic recrystallisation is completed, the alloy is in a steady state and further deformation of the alloy cannot change the grain size. The multitemperature MAF procedure can produce a fine-grained AZ61 alloy giving a grain size of 8 μm. This fine-grained alloy has an excellent strength accompanied by reasonable good tensile ductility. The success of the development of this multitemperature MAF procedure proves that MAF can offer a good opportunity for the development of magnesium alloys with good mechanical properties. © 2012 Elsevier B.V.


Chen Q.,Southwest Technique and Engineering Institute | Shu D.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Wang Y.,Southwest Technique and Engineering Institute | Yuan B.,Hefei University of Technology
Materials and Design | Year: 2012

The Mg-5.3. wt.%Zn-1.13. wt.%Nd-0.51. wt.%La-0.28. wt.%Pr-0.79. wt.%Zr alloy prepared by direct chill casting is subjected to hot extrusion. The effects of extrusion ratio and temperature on microstructure and tensile mechanical properties have been studied. The results indicate coarse grains of as-cast alloys are refined with extrusion ratio increasing from 0 to 9. The eutectic constituents are elongated along extrusion direction. However, further increase of extrusion ratio has a little influence on grain refinement and the improvement of mechanical properties of the alloy. Dynamic recrystallisation is the main mechanism of grain refinement during hot extrusion. Raising extrusion temperature results in grain coarsening. Grain shape becomes more equiaxed-like with raising extrusion temperature. At the same time, mechanical properties decrease with the increase of extrusion temperature. © 2012 Elsevier Ltd.


Chen Q.,Southwest Technique and Engineering Institute | Huang Z.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Shu D.,Southwest Technique and Engineering Institute
Solid State Communications | Year: 2013

Elastic properties, thermodynamics and electronic structures of MgNi 2, MgCu2, MgZn2, Mg2Y and Mg 2La have been determined from first-principle calculations. The elastic constants are calculated, the calculated bulk moduli B, shear moduli G, Young's moduli E, Poisson ratio ν and elastic anisotropy AU show that MgNi2, MgCu2, MgZn2 and Mg2Y are ductile, while Mg2La is brittle; the stiffness of MgNi 2 is the largest; MgZn2 is of the best plasticity among five phases; MgCu2 has the most anisotropy. Debye temperature, enthalpy, free energy, entropy and heat capacity are calculated and discussed. The calculated densities of states (DOS) show that MgZn2 has the strongest structural stability. The ionicity and metallicity of the phases is estimated, MgCu2 has the strongest ionicity and the metallicity of Mg2Y is the best. © 2013 Elsevier Ltd.


Chen Q.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Hu C.,Southwest Technique and Engineering Institute | Shu D.,Southwest Technique and Engineering Institute
Journal of Alloys and Compounds | Year: 2011

Thixoextrusion involves processing alloys with a spheroidal microstructure in the semi-solid state. Before thixoextrusion, repetitive upsetting-extrusion (RUE) is introduced into the strain induced metal activation (SIMA) process to predeform AZ80 magnesium alloy. Microstructure evolution of RUE formed AZ80 magnesium alloy during partial remelting is studied at temperatures for times. Tensile mechanical properties of thixoextruded components are determined and compared with those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. The results show that with increasing number of RUE passes solid grain size decreases and the rate of liquation is improved. Prolonged holding time results in grain coarsening and the improvement of degree of spheroidization. The variation of the solid grains with holding time obeys the Lifshitz, Slyozov and Wagner law. Increasing the heating temperature is favorable for the formation of spheroidal solid grains. The tensile properties for AZ80 magnesium alloy thixoextruded from starting material produced by RUE are better than those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. © 2011 Elsevier B.V. All rights reserved.


Chen Q.,Southwest Technique and Engineering Institute | Zhao Z.,Southwest Technique and Engineering Institute | Shu D.,Southwest Technique and Engineering Institute
Materials Science and Engineering A | Year: 2011

Based on conventional extrusion and equal channel angular extrusion (ECAE), a new severe plastic deformation (SPD) method called compound extrusion is developed to fabricate fine-grained AZ91D magnesium alloys. The fine grain size of 6 μm is obtained as the accumulated strain increased to 9.146. The AZ91D alloy treated by compound extrusion exhibits good mechanical properties, with a yield strength of 202.2. MPa, a tensile strength of 323.1. MPa and an elongation to fracture of 14.8%. The good mechanical properties of AZ91D alloy treated by compound extrusion are due to grain refinement and to the homogeneous distribution of intermetallic particles. The success in development of compound extrusion proves that compound extrusion can offer a good opportunity for the development of good mechanical properties of as-cast magnesium alloys. © 2011 Elsevier B.V.

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