Lu Shiqiang

Hot deformation mechanism and process optimization for ti-alloy ti-6.5al-3.5mo-1.5zr-0.3si during α+β forging based on murty criterion

Abstract To investigate the hot deformation and optimize the process configuration for Ti-alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si in α+β forging process, the processing maps (P-maps) are developed for the alloy with α+β microstructure based on Murty instability criterion. The P-maps are constructed by the experimental results obtained through the isothermal and constant strain rate compression test at the temperatures of 780–990 °C and the strain rates of 0.001-70 s−1. The relationship between the deformation mechanism as well as deformation defect and deformation thermomechanical parameter is studied by the generated P-maps. The results show that the superplasticity deformation would occur at the temperature range of 780–990 °C and the strain rate range of 0.001-0.01 s−1. In addition, flow instability including cracks and cavities in β phase, flow localization and adiabatic shear bands would occur at the above mentioned temperature range under the strain rates greater than 0.01 s−1. According to the P-maps, microstructure and flow stress status, the preferred deformation thermomechanical parameters are identified, e.g. the temperature range of 850–940 °C and the strain rate range of 0.001-0.01 s−1. The optimum deformation thermomechanical parameter is around the temperature of 900 °C and the strain rate of 0.001 s−1.

Twinning and Softening of Cast Magnesium Alloy AZ91 under Hot Compression

Cast magnesium alloy AZ91 is studied after uniaxial compression in the range from room temperature to 400°C. The alloy is tested for compression and its microstructure is determined. The values of the parameter of strain hardening are found. The main mechanisms of structural transformations developing under compressive deformation of alloy AZ91 at low and moderate temperatures are considered.

The effect of microstructure and the related bio-corrosion behavior of AZ91D Mg alloy in SBF artificial body fluid

Purpose – The effect of SBF artificial body fluid on microstructure and morphology characteristics of AZ91D alloy was investigated using OM, SEM and XRD. The effect of corrosion on mechanical properties also was researched. Design/methodology/approach – The results show that the corrosion weight loss rate initially increased, then clearly decreased, and finally remained steady. Pits began to appear when the sample was placed in a corrosive environment for five days and pitting gradually increased with longer exposure time. Findings – The pits, which made the grain boundaries indistinct, first appeared near the grain boundary area and then gradually increased in area. Originality/value – The main mode of corrosion is pitting and the primary corrosion product, MgOH2, could be observed after five days of corrosion.

Effect of Ecap by Routes B c and C on the Microstructure and Temperature of Martensitic Transformation of NitiNb Alloy

The structure of a NiTiNb shape memory alloy is studied after equal channel angular pressing (ECAP) by routes Bc and C. The mechanisms of straining of the alloy after the ECAP are analyzed. The temperatures of martensitic transformations are determined by the method of differential scanning calorimetry as a function of the route of the ECAP.