Sufen Xiao

Study on microstructure and mechanical properties of as-cast Mg-Sn-Nd alloys

Abstract Microstructure, tensile properties and compressive creep behaviors of Mg-(1.65–11.52) wt.% Sn-2 wt.% Nd alloys were studied in this paper. The microstructure of the as-cast Mg-Sn-Nd alloys consisted of dendritic α-Mg, Mg 2 Sn and Mg-Sn-Nd ternary phase containing rare earth element. The highest ultimate tensile strength of 140 MPa and percentage elongation after fracture of 9.7%, were achieved with a composition of Mg-8.23 wt.% Sn-2 wt.% Nd. The compressive creep resistance of Mg-8.23 wt.%Sn-2 wt.% Nd alloy was much better than other alloys at 200 °C for applied load of 35 MPa, which was mainly due to the formation of dispersive heat-resistance Mg 2 Sn and Mg-Sn-Nd intermetallic compounds.

Microstructure, tensile properties and compressive creep resistance of Mg-(5–8.5)%Sn-2%La alloys

Abstract The microstructure, tensile properties and compressive creep resistance of permanent-mould cast Mg-(5–8.5)%Sn-2%La (mass fraction) alloys were investigated. The results show that Mg-(5–8.5)%Sn-2%La alloys are all composed of α -Mg phase, Mg 2 Sn and Mg-La-Sn compounds. Compared with those of Mg-5%Sn binary alloy, the grain size and the content of Mg 2 Sn compound in Mg-5%Sn-2%La alloy are decreased. With the increase of Sn content in Mg-(5–8.5)%Sn-2%La alloys, the content of Mg 2 Sn compound increases, while that of Mg-Sn-La compound changes little. In addition, the investigation suggests that the thermally stable Mg-Sn-La and Mg 2 Sn compounds can improve the tensile properties and compressive creep resistance of the alloys.

Sintering densification of titanium hydride powders

ABSTRACT The sintering densification behaviors of titanium hydride are investigated at different compaction pressures, compared with pure titanium. The results show that the shrinkage and densification of the TiH2 specimens after sintering are obviously higher than those of pure Ti. It is also found that the densification mechanism of the TiH2 is mainly attributed to the volume change in the TiH2 sintering process, and the surface cleaning effect of the released H atoms. In addition, it is also validated experimentally that the released H atoms are accompanied by the formation of H2O, which reduces the oxide film on Ti surface, increases the chemical activity of the Ti surface, and promotes the sintering densification.

Compressive creep behavior of Mg-Sn binary alloy

Mg-Sn based alloy is one of the potential alloys for application at elevated temperature. The compressive creep behavior of ageing-treated Mg-χSn (χ=3%, 5%) alloys was investigated at the temperatures of 423 and 473 K and the stresses from 25MPa to 35MPa. When the tin content varies, the ageing-treated Mg-χSn alloys show quite different creep resistance, which are mainly attributed to the size and distribution of Mg2Sn phases in the ageing-treated Mg-χSn alloys. The calculated value of stress exponent, n=6.3, suggests that the compressive creep behavior of the ageing-treated Mg-5%Sn alloy is controlled by dislocation creep at the temperature of 473 K and the stresses from 25MPa to 35MPa.

Fabrication of low-cost Ti-1Al-8V-5Fe by powder metallurgy with TiH2 and FeV80 alloy

ABSTRACT The low-cost Ti-1Al-8V-5Fe (Ti-185) alloy with a high strength is prepared by cold-compaction-and-sintering powder metallurgy process with low-cost titanium hydride (TiH2) powders and FeV80 master alloy powders. The use of simple technique process and cheap alloying elements can lead to the cost reduction for titanium alloys. The thermal decomposition of TiH2-1Al-8V-5Fe is analyzed by thermal gravimetric analyses and differential scanning calorimetry simultaneous thermal analyzer. The shrinkage behavior of TiH2-1Al-8V-5Fe during the sintering process is employed by the high-sensitivity dilatometer system. The microstructure of sintered Ti-185 consists of β-phase and lamellar α-phase. The results show that the sintered Ti-185 alloys have the relative density of 97.8%, homogeneous composition, and fine grains. The yield strength and the hardness are 1461 MPa and 40.1 ± 1.0 HRC (unit of Rockwell hardness), which are better than that of as-cast Ti-185.

TiH2-based Ti-1Al-8V-5Fe PM alloys with different addition methods of alloying elements

ABSTRACT The powder metallurgy high-strength Ti-1Al-8V-5Fe alloy (Ti-185 alloy) was investigated in this paper with different addition methods of alloying elements, Al, V, Fe pure elements powder (EP) or 1Al-8V-5Fe ternary master alloy powder (MAP), based on TiH2 powders at the sintering temperature from 1150 to 1350°C. The results indicate that the Ti-185 alloy with the 1Al-8V-5Fe master alloy (Ti-185 MAP alloy) possesses the higher relative sintered density, less oxygen content, and less α-phase volume fraction versus the Ti-185 alloy with Al, V, and Fe pure elements (Ti-185 EP alloy). No matter where the sintering temperature is 1150, 1250, or 1350°C, Ti-185 MAP alloy invariably has the higher yield strength and hardness which have a strong relationship to its higher density and less volume fraction of softer α-phase in comparison with Ti-185 EP alloy.

Effect of precipitates on thermal conductivity of aged Mg-5Sn alloy

Abstract The influence of precipitates on thermal conductivity of aged Mg-5Sn alloy has been investigated at different heat treatment temperatures. The results show that the thermal conductivity of aged Mg-5Sn alloy increases from 87.5 to 92.8 W·m−1·K−1 at 433 K for 720 h and from 87.5 to 122 W·m−1·K−1 at 513 K for 120 h with the increasing ageing time. The increasing rate of the former is obviously lower than that of the latter. Meanwhile, the Sn content of precipitates at 433 K is considerably below that of aged Mg-5Sn at 513 K. The interface between precipitates and α-Mg matrix is completely coherent at 433 K for 720 h. The increase in thermal conductivity is mainly attributed to the remaining Sn solutes in α-Mg matrix, and the interface relationship between precipitates and α-Mg matrix.

Microstructure and mechanical properties of as-cast Mg-5Sn-2Ce- x Zn alloys

Abstract The microstructure, mechanical properties and compression creep resistance of as-cast Mg-5Sn-2Ce- x Zn ( x =0, 2 wt.%, 4 wt.%) alloys were investigated in this paper. The results showed that the Ce-containing compounds were MgSnCe phase and an unknown phase, and they were the dominant intermetallics in as-cast Mg-5Sn-2Ce- x Zn alloys. At x =0 wt.%, the Ce-containing compounds formed in interdendritic regions with the shape of rod. As the Zn content was increased to 2 wt.%, the Ce-containing compounds partly changed from rod-like to sheet-like. However, there were few further changes in the Ce-containing compounds with further increase in Zn content to 4 wt.%. Compared with Mg-5Sn-2Ce alloy, the tensile strength and elongation of the alloy containing 4 wt.% Zn increased by 39% and 112%, respectively, and the secondary creep rate (175 °C/55 MPa) decreased at least by an order of magnitude. These improvement could be attributed to the combined effects of the high content of Zn dissolving in α-Mg matrix and the modification of Ce-containing compounds by Zn addition.

Magnetic properties and magnetic exchange interactions in Gd1–xREx(RE=Pr, Nd) alloys

The effect of Pr, Nd addition on the magnetic properties and magnetic exchange interaction of gadolinium alloys was systematically studied. Curie temperature TC and magnetic moment of Gd1–xREx (RE=Pr, Nd) systems with x<0.05 were investigated. When x<0.05, Pr and Nd formed respectively with Gd continuous solid solution which has the crystalline structure HCP. Study on the magnetic behavior indicated that at near room temperature, the simple ferromagnetism prevailed in these two systems of alloy. The Curie temperature and magnetic moment of Gd1–xREx alloy decreased with RE (RE= Pr, Nd) content x increasing. The de Gennes factor of Gd1–xREx alloy which was associated with the exchange interaction between magnetic spin components also decreased with RE content increasing. The above results showed that the magnetic exchange interaction between magnetic atoms in gadolinium could be effectively changed by the Pr, Nd addition.

The powder metallurgy performance of Ti-1Al-8V-5Fe alloys with unsaturated titanium hydride

ABSTRACT The high-strength Ti-1Al-8V-5Fe alloy is synthesized with separately unsaturated titanium hydride, TiH1.5, powders and saturated titanium hydride, TiH2, powders, via cold compaction and sintering powder metallurgy process. The results show that the Ti-185 alloys with TiH2 or TiH1.5 powders have similar mechanical performances after compacted at 1000 MPa and sintering at 1350°C for 2 h. Whereas Ti-185 alloy based on TiH1.5 presents better economically advantageous and compressive formability, and the sintered density is 4.58 g cm−3 (relative density is 98.5%), which is a potential candidate to prepare high-densification and low-cost Ti-185 alloy in the future market.