Yandong Jia

Hot deformation behavior of spray formed Al-22Si-5Fe-3Cu-1Mg alloy

Abstract The hot deformation behavior of a spray formed Al-22Si-5Fe-3Cu-1Mg alloy was investigated by isothermal compression tests at temperature ranging from 350°C to 500°C and strain rate from 0.001 s−1 to 0.1 s−1. At the beginning of deformation, work hardening is the major factor. The flow stress quickly reaches a peak, followed by a continuous reduction, then a balance is established between the tendency to work harden and the tendency to flow soften. The stress curves appear almost in flat shape. A constitutive equation in the hyperbolic sine function for describing the deformation behavior was established and the hot deformation activation energy was determined to be 312.65 kJ/mol. It can be concluded that the temperature of extrusion should not be more than 500°C in order to avoid primary silicon coarsen.

The Formation Mechanism of Porosity for Spray-deposited 7075 Alloy

The distribution model of temperature for the billets was established based on the porosity formation mechanism. By calculating the numerical relationship between the temperature of the deposition layer and the formation ability of the porosity, the distribution of porosity for spray formed 7075 aluminum billets was predicted and the influence of superheat on the formation probability of porosity was analyzed. The results show that a denser billet can be obtained with the average temperature of 813 K of the droplets and a liquid fraction of 50%. The porosity would increase whether the temperature further increased or decreased. Finally, the 7075 aluminum alloy was prepared by spray deposition technique with the optimum process parameters. It can be found that the distribution and types of the porosity were different at different locations. These results are in good agreement with the porosity distribution law.

Microstructure Evolution and Mechanical Properties of Spray-deposited Al-21.47Si-4.73Fe-2.5Cu-0.9Mg Alloy

Al-Si-Fe-Cu-Mg alloy was prepared by spray deposition and was further processed by hot extrusion as well as T6 heat-treatment. The results indicate that the microstructure of the deposited alloy is composed of primary Si particles with average size of less than 5 μm, α-Al, Al2CuMg, ß-Al5 FeSi and δ-Al4 FeSi2 (rectangular shape) , and no eutectic silicon is found due to the special solidification behavior. The age hardening curves reveal two peaks. The uniform ultimate tensile strength (UTS) and the elongation of the peak-aged Al-Si-Fe-Cu-Mg alloy are 468. 3 MPa, 0. 61% at 298 K and 267. 4 MPa, 6. 42% at 573 K, respectively. The fracture surfaces display brittle fracture morphology at 298 K, whereas it varies to mixture of brittle and ductile failure with increasing the temperature.

Comparative Study of Magnetic Properties and Microstructure for As-cast and Square-wave Pulse Current Joule Annealed Wires

We here report on a comparative study of the microstructure and magnetic properties of as-cast and SPCJA-ed Co-based wires for potential sensor applications. Experimental results indicate that both as-cast and SPCJA-ed wires exhibit typical amorphous feature. There also exists the enhanced local ordering degree of atomic arrangement and obvious transformation (maximum magnetic permeability and minimum saturation magnetization) of magnetic properties after SPCJA treatment, resulting from variation of magnetic moment exchange coupling and magnetic anisotropy by coactions of high-density pulsed magnetic field energy and thermal activation energy. Moreover, SPCJA treatment can drastically improve the GMI property of melt-extracted wires. GMI ratio [ΔZ/Z0]max of 166.07% and field response sensitivity ξmax of 413.76%/Oe by more than 2.25 times and 1.73 times of as-cast wire at 5MHz. Therefore, the SPCJA-ed wire exhibits the improved GMI and magnetic properties at 5MHz~10MHz in contrast to AC annealed wire, which is more suitable for GMI sensor applications working at low-applied-frequency and relatively low-working-magnetic field.