Zesheng Ji

Microstructure and mechanical properties of AZ31-Ce prepared by multipass solid-phase synthesis

ABSTRACT The effects of extrusion passes on the microstructure and mechanical properties of the magnesium AZ31-Ce alloy prepared by solid-phase synthesis were studied. The deformation mechanism of Mg-Ce chips was also discussed. The alloy was characterised by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry and an electronic universal strength tester. The results show that Mg-Ce chips are constantly crushed and deformed, and finally exhibit a fine granulated shape as the number of extrusion passes increases. The mechanical properties of the alloy markedly increase with further extrusion passes. After five passes, the tensile strength and elongation reach 311 MPa and 9.83%, respectively. The solid-phase synthesis method has the potential to prepare wrought magnesium alloys with rare earth alloying additions.

Evaluation of microstructure and properties of AZ31/Al2O3 composites prepared by solid-phase synthesis

ABSTRACT Solid-phase synthesis was used to prepare AZ31/Al2O3 composites and the effect of Al2O3 particles on its microstructure and mechanical properties was investigated. The composites were characterised by optical microscopy, scanning electron microscopy, transmission electron microscopy, vickers hardness tester and electron universal strength tester. The results show that the grains of the composites are significantly refined and the mechanical properties increase obviously. While the content of Al2O3 particles is 2 wt-%, the hardness, ultimate tensile strength and elongation to failure reach the maximum of 85HV, 308 MPa, 6.83%, respectively. The addition of Al2O3 particles promotes the dynamic recrystallisation.

Formation and Growth Mechanism of Globular Crystal of ADC12 Aluminum Alloy by Near-Liquidus Squeeze Casting

A new method of near-liquidus squeeze casting (NLSC), which obtains globular crystal, has been developed. The research focuses on the formation and growth mechanism of globular crystals of ADC12 alloy by NLSC. Globular crystal transforms into rosette crystal, average grain size (AGS) increases, and average globular coefficient (ASC) decreases with the rise of pouring temperature. But AGS decreases to 17.8 μm directly and ASC increases directly to 0.46 when the pouring temperature is 650°C. NLSC globular crystal of different sizes (AGS is 22.5 μm; ASC is 0.73) distributes uniformly in matrix. Heterogeneous nucleation grows on the solid particles of metal walls and fusing grains. The formation and growth modes of globular crystal include normal grain growth, annexation of small globular crystal, and fracture and spherulization of rosette crystal. NLSC globular crystal critical radius is inversely proportional to degree of supercooling. The pressure has very little influence on critical radius by increase of melting point and thermal conductivity, but it affects critical radius greatly by changing the degree of supercooling. NLSC globular crystal has no enough time to exceed the critical radius.

Semi-solid microstructure of AZ91D magnesium alloy recycled from waste chips during heat treatment

In this paper, waste chips of AZ91D magnesium alloy were recycled to prepare semi-solid billets. The chips were hot compressed into billets. And then, the billets were subjected to a series of isothermal heat treatment for various holding times. Its semi-solid microstructure evolution was investigated during heat treatment. A semi-solid microstructure with highly spheroidal and homogeneous primary particles can be obtained after partially remelting. With increasing heating temperature, the diffusion of Al element from eutectic Mg17Al12 phase to α-Mg first took place, resulting in the primary dendritic grains coarsening into interconnected non-dendritic grains. With heating continuously, the residual interdendritic γ-Mg17Al12 at the edges of the primary grains melted in succession and the primary grains separated into small polygon grains. Increasing the heating temperature can reduce the solid volume fraction. During the semi-solid isothermal treatment, with the increasing of the holding time, the solid particles became more globular and the amount of liquid increased until the solid-liquid system reached its equilibrium state. At the same time, owing to the decreasing of interfacial energy and the effect of interfacial tension, the particles gradually spheroidized and began to grow with a further increasing of the holding time.