Zhongtao Jiang

Microstructural Evolution of Mg-4Al-2.5Ca Alloy during Solidification

In the present work, the microstructure evolution of Mg-4Al-2.5Ca alloy during solidification was investigated by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and differential scanning calorimetry (DSC). The results showed that the as-cast microstructure was typical dendritic structure, consisting of α-Mg and the Al2Ca with a C15 structure formed at inter-dendritic regions. But during slow solidification, the sequence of phase formation of this alloy consisted of following stages: L→ L + α-Mg → L + α-Mg + (Mg, Al)2Ca → α-Mg + (Mg, Al)2Ca + Al2Ca → α-Mg + Al2Ca. Thermal analysis showed that the (Mg, Al)2Ca and Al2Ca phase separation temperature was about 520°C and 510°C respectively, which is different from thermodynamic calculation. With the temperature decreasing, the liquid (Mg, Al)2Ca phase with thick and continuous morphology transformed into lamellar-shaped eutectic phase, and parts of (Mg, Al)2Ca phase translated into Al2Ca phase with bone-shaped and needle-like.

Preparation and Characterization of Magnesium Alloy Containing Al2Y Particles

A magnesium alloy containing Al2Y particles was successfully fabricated by changing the content of Al in the Mg-6Y alloy melt. Its microstructure and mechanical properties were subsequently characterized. The results show that two types of Al2Y particles were discovered in the Mg-6Y-xAl (x = 0.5–5) alloys, which are namely the polygonal particles in the pre-precipitated phase and the discontinuous network of particles in the eutectic phase. With an increase in Al content, the amount of pre-precipitated Al2Y increases and the eutectic decreases gradually. When the Al content is 5 wt %, Al2Y particles are almost all in the pre-precipitated phase in the Mg-6Y alloy. After hot extrusion, the YA65 alloy could be regarded as the Mg master alloy that contains Al2Y particles with heterogeneous nucleation capability or Al2Y particle-reinforced magnesium matrix composites. The tensile strength of the as-extruded magnesium alloy is significantly improved at ambient temperatures.

Effect of SiO2 nanoparticles as lubricating oil additives on the cold-rolling of AZ31 magnesium alloy sheet

Abstract Magnesium alloy sheets were processed by cold rolling without lubrication and with SiO2 nanolubricant so as to investigate cold rolling performance by measuring rolling force as well as the surface roughness of the sheets. A series of ball on disc tests without lubrication and with SiO2 nanolubricant conditions were carried out to simulate the contact and sliding during the cold rolling process. The results indicate that the SiO2 nanolubricant effectively reduced the rolling force and improved the surface quality of sheets by SiO2 nanolubricant during cold rolling process. The excellent cold-rolling performances of AZ31 Mg alloy with SiO2 nanolubricant were attributed to the friction-reducing and the anti-friction mechanism was based on the deposition of nanoparticles on the magnesium alloy surfaces.