R.F. Zhang

Effects of sodium tungstate on properties of micro-arc coatings on magnesium alloys

Abstract Anodic coatings were prepared by micro-arc oxidation on AZ91HP magnesium alloys in a base solution containing 10 g/L NaOH and 12 g/L phytic acid with addition of 0–8 g/L sodium tungstate. The effects of sodium tungstate on the coating thickness, mass gain, surface morphology and corrosion resistance were studied by eddy current instrument, electronic scales, scanning electron microscope and immersion tester. With the addition of sodium tungstate, the electrolytic conductivity increases and the final voltage decreases. The sodium tungstate has a minor effect on the coating thickness, but lightens the coating color. With increasing sodium tungstate concentration, the size of micropores on the coatings is enlarged and the corrosion resistance of the anodized samples decreases.

Effect of annealing processing on microstructure and properties of Ti-6Al-4V alloy by powder injection molding

Abstract Ti6A14V alloy parts were prepared by metal injection molding. Brown parts were densified at 1 200–1 260°C for 2–4 h in vacuum atmosphere. The as-sintered specimens were treated through Hot-Isostatic Pressure(HIP) at 960 °C and 140 MPa. Ti6A14V alloy compacts were annealed at 720–760 °C for 1 h. The results show that binder in the parts can be removed by solvent debinding and thermal debinding process. Ti6A14V alloy has an uniform duplex microstructure with many equiaxed α grains and a little β grains. When the annealing temperature is higher than 800 °C, Ti6A14V alloy has lower mechanical properties. After solution treatment and aging, a typical martensite microstructure can be achieved.

Effects of electric parameters on corrosion resistance of anodic coatings formed on magnesium alloys

Abstract Anodic coatings were obtained by micro-arc oxidation on AZ91HP magnesium alloys in a solution containing 10 g/L NaOH and 8 g/L phytic acid. The effects of electric parameters including frequency, final voltage, duty cycle and current density on the corrosion resistance of anodic coatings formed on the magnesium alloys were investigated by using an orthogonal experiment of four factors with three levels. The results show that the final voltage plays a main role on the coating properties. The orders of affecting corrosion resistance and coating thickness are separately ranked from high to low as, final voltage>duty cycle>current density>frequency and final voltage>current density>frequency>duty cycle. The final voltage influences the corrosion resistance of the anodized samples mainly by changing the surface morphology and coating thickness.

Stress-induced martensitic transformation in (Ni47Ti44)100-xNbx shape memory alloys with wide hysteresis

The effect of deformation via stress-induced martensitic transformation on the reverse transformation behavior of the (Ni47Ti44)(100-x)Nb-x(x=3, 9, 15, 20, 30, mole fraction, %) shape memory alloys was investigated in detail by differential scanning calorimetry (DSC) after performing cryogenic tensile tests at a temperature of M-s+30 degrees C. The results show that Nb-content has obvious effect on the process of stress-induced martensitic transformation. It is also observed that the stress-induced martensite is stabilized relative to the thermally-induced martensite (TIM) formed on cooling, and Nb-content in Ni-Ti-Nb alloy has great influence on the reverse transformation start temperature and transformation temperature hysteresis of stress-induced martensite(SIM). The mechanism of wide transformation temperature hysteresis was fully explained based on the microscopic structure and the distribution of the elastic strain energy of (Ni47Ti44)(100-x)Nb-x alloys.