Rongshi Chen

Preparation of calcium phosphate coatings on Mg-1.0Ca alloy

The calcium phosphate coatings were prepared by virtue of electrochemical deposition in order to improve the corrosion resistance of Mg-1.0Ca alloys in simulated body fluids. The chemical compositions, structures and morphologies of the coatings were investigated by energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively. The potentiodynamic electrochemical technique was employed to investigate the bio-degradation behavior of Mg-1.0Ca alloys with Ca-P coatings in Hanks solutions. The experimental results show that the deposited coatings predominately consist of flake-shape brushite (DCPD, CaHPO(4)center dot(2)H(2)O) crystallites. The corrosion resistance of the substrates with coatings is improved in Hanks solutions significantly.

Key R&D activities for development of new types of wrought magnesium alloys in China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies. The research activities are funded primarily through four government-supported programs: the Key Technologies R&D Program of China, the National Basic Research Program of China, the National High-tech R&D Program of China, and the National Natural Science Foundation of China. The key R&D activities for the development of new wrought magnesium alloys in China are reviewed, and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys. Some novel plastic processing technologies, emerging in recent years, which aim to control deformation texture and to improve plasticity and formability especially at room temperature, are also introduced.

Microstructures and mechanical properties of cold rolled Mg-8Li and Mg-8Li-2Al-2RE alloys

Abstract The microstructures and mechanical properties of Mg-8Li and Mg-8Li-2Al-2RE alloy sheets were evaluated after cold rolling. Both alloys contain α-phase and β-phase which consists of a solid solution of Mg in BCC Li. The proportion of β-phase in both alloys is approximately 60%. The α-phase and β-phase are elongated approximately parallel to the rolling direction and there is no sign of recrystallization even after being annealed at 200 °C for 1 h. The yield strength of Mg-8Li-2Al-2RE sheets is about 165 MPa with elongation of 35% along rolling direction, while the yield strength is about 187 MPa with elongation of 21% along the direction titled 45° to rolling direction. The α-phase in both alloys exhibits basal texture, and the intensity of basal texture in Mg-8Li is larger than that in Mg-8Li-2Al-2RE. However, the β-phase shows (100) texture, and the intensity of (100) texture in Mg-8Li is twice of that in Mg-8Li-2Al-2RE. It could be attributed to the existence of RE-containing particles in Mg-8Li-2Al-2RE.

Microstructure and Mechanical Properties of Mg-Gd-Y-Zr Alloy Cast by Metal Mould and Lost Foam Casting

The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr (mass fraction, %) alloy (GW104 alloy) cast by metal mould casting (MMC) and lost foam casting (LFC) were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of alpha-Mg solid solution, eutectic compound of alpha-Mg+Mg(24)(Gd, Y)(5) and cuboid-shaped Mg(5)(Gd, Y) phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 degrees C for 6 h, while the Mg5(Gd, Y) phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.

Study on electroless Ni-P-ZrO2 composite coatings on AZ91D magnesium alloys

Abstract Electroless Ni–P–ZrO2 composite coatings on AZ91D magnesium alloys was developed and their characteristics were investigated. The experimental results showed that the composite coatings were uniform and compact. The hardness of Ni–P–ZrO2 composite coatings reached the maximum value at 350°C heat treatment, and then decreased at 400°C. The nickel phosphor alloys provided solution strengthening and precipitation strengthening, while the ZrO2 nanoparticles provided dispersion hardening, making the composite coatings harder than that of Ni–P coatings. The wear resistance of Ni–P–ZrO2 composite coatings was obviously superior to Ni–P coatings, especially with longer wear time, which can be attributed to the dispersion strengthening and load support effect of ZrO2 in the coatings. The Ni–P–ZrO2 coatings exhibited better corrosion resistance than that of Ni–P coatings owing to codeposition of ZrO2 together with NiP leading to a more compact composite coating.

Enhancement of ductility in high strength Mg-Gd-Y-Zr alloy

A high strength GW94 alloy with fully recrystallized microstructure and equiaxed ultrafine grains of submicron size was produced by multiaxial forging and ageing. The alloy exhibits an ultimate tensile strength of 377 MPa, proof stress of 295 MPa and elongation to failure of 21.7%. The ductility is improved in comparison with that of the conventional extrusion processing. Superplastic ductility is achieved in tensile testing at 573 K with a maximum elongation of 450%. These high ductility and high strength are attributed to the coexistence of fully recrystallized grains and nanoscale Mg(5)(Gd, Y) particles dynamically precipitated at grain boundaries.

Microstructural evolution and enhanced superplasticity in friction stir processed Mg–Zn–Y–Zr alloy

[Xie, G. M.; Ma, Z. Y.; Chen, R. S.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Xie, G. M.; Geng, L.] Harbin Inst Technol, Sch Mat Sci & Engn, Harbin 150001, Peoples R China.;Ma, ZY (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;zyma@imr.ac.cn

Strength enhancement of Mg-3Gd-1Zn alloy by cold rolling

Abstract The severe cold rolling was employed to enhance strength of Mg–3Gd–1Zn (mass fraction, %) alloy sheet. The 0.2% yield stress of the Mg–3Gd–1Zn hot-rolled sheet can be increased by 150% through the single-pass cold rolling with the reduction of 23%, due to the high intensity of dislocation and basal texture established during cold rolling. Compared with the Mg-3Gd-1Zn hot-rolled sheet, the cold-rolled sheet annealed at 350°C for 30 min may get an enhancement in strength without a great loss of ductility. The sheet processed by multi-pass cold rolling does not show a higher strength as expected, due to the softening effect of shear bands. However, the thin slab with the thickness less than 1 mm can be produced by the multi-pass cold rolling with the annealing treatment as few as possible.

Superplasticity of a multiphase Ni-25Al-25Cr intermetallic alloy

In the past decade significant improvement in high temperature strength, processing and design methodology for NiAl have been achieved. However, limited ductility and toughness as well as poor impact resistance continue to be critical issues which will impede near term production implementation. The most recent work on NiAl suggests that the room toughness of NiAl can be conveniently improved in-situ with refractory metal phases by directional solidification of pseudo-binary (e.g., NiAl-Cr) and -ternary(NiAl-Cr(Mo)) eutectic systems. Since it has been well established that the majority of eutectic alloys, such as Al-Cu, Al-Si and Al-Al{sub 3}Ni, display superplasticity under appropriate conditions, their enthusiasm for exploring whether the multiphase Ni-25Al-25Cr alloy, containing a ternary eutectic of {beta}Ni(Al,Cr) + {gamma}{prime}Ni{sub 3}(Al,Cr) is appropriate.

Fracture behavior of high strength Mg-Gd-Y-Zr magnesium alloy

The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr (mass fraction, %) (GW94) alloy was investigated under different thermal conditions, including as-cast, solution-treated, peak-aged, and over-aged states. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to examine the crack nucleation and fracture model. The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature, the fracture model of the as-cast GW94 alloy is quasi-cleavage, while that of the solution-treated alloy is transgranular cleavage. It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions. Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300 degrees C, corresponding to the intergranular fracture. Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300 degrees C.