Semi-solid Isothermal Treatment Research Articles

Preparation of Semi-Solid Billet of ZW61 Alloy by Equal Channel Angular Extrusion

Strain induced and melt activated (SIMA) is used for the preparation of semi-solid billet through equal channel angular extrusion (ECAE) as strain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment, by which semi-solid billet with fine spherical grains can be prepared. As comparison, extruded ZW61 alloy is also remelted to the semi-solid state. Furthermore, both of the semi-solid isothermal treatment microstructures in as-cast and extruded ZW61 alloy are discussed. ECAE process is found more potential for semi-solid thixoforming for as-cast ZW61 alloy.

Effects of holding temperature and time on semi-solid isothermal heat-treated microstructure of ZA84 magnesium alloy

The feasibility of fabricating ZA84 magnesium alloy with non-dendritic microstructure by a semi-solid isothermal heat treatment process and the effects of holding temperature and time on the semi-solid isothermal heat-treated microstructure of the alloy were investigated. The results indicate that it is possible to produce ZA84 alloy with non-dendritic microstructure by suitable semi-solid isothermal heat treatment. After being treated at 560-575 °C for 120 min, ZA84 magnesium alloy can obtain a non-dendritic microstructure with 14.2%-25.6% liquid fraction and an average size of 56-65 μm of the unmelted primary solid particles. With the increasing holding time from 30 to 120 min or holding temperature from 560 to 575 °C, the average size of unmelted primary solid particles decreases and globular tendency becomes more obvious. Under the experimental condition, the microstructural evolution of ZA84 alloy during semi-solid isothermal treatment is mainly composed of three stages of initial coarsening, structural separation and spheroidization. The subsequent coarsening of spheroidal grains is not observed.

Compression Deformation Behavior of AZ91D Magnesium Alloy in Semi-Solid State

The semi-solid compression deformation behavior of the AZ91D alloy with non-dendritic structure, which was obtained under the semi-solid isothermal treatment condition of 570°C×60min, was studied by means of Gleeble-1500 thermal-mechanical simulator. When the compression strain was lower than 0.7, along with the compression strain increasing, the compression stress firstly increased rapidly, then decreased rapidly, and finally kept a constant stress level gradually. Under the condition of different deformation temperatures and deformation rates, the maximum compression stress was obtained simultaneously when the compression strain value was 0.025 approximatively. Furthermore, when the deformation rate kept a constant, the compression stress decreased along with the deformation temperature increasing, and when the deformation temperature kept a constant, the compression stress increased along with the deformation rate increasing.

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angular extrusion to magnesium alloy. The results show that mechanical properties of AZ91D alloy at room temperature, such as yield strength(YS), ultimate tensile strength(UTS) and elongation, are enhanced greatly by four-pass equal channel angular extrusion(ECAE) at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20 βm. Through using ECAE as strain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment, semi-solid billet with fine spheroidal grains of 25 βm can be prepared successfully. Compared with common SIMA, thixoformed satellite angle frame components using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and high temperature of 373 K.

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that with increasing semi-solid isothermal treatment temperature, the α phase solid grain size of processed Mg-Al-Zn alloy by ECAE increases firstly due to coarsening of α phase solid grains, then decreases due to melting of α phase solid grains. With the increase of extrusion passes during ECAE, the α phase solid grain size in the following semi-solid isothermal treatment decreases. The α phase solid grain size of processed Mg-Al-Zn alloy by ECAE under route B c is the smallest, while the α phase solid grain size of processed material by ECAE under route A is the largest. The primary mechanism of spheroid formation depends on the melting of recrystallizing boundaries and diffusion of solute atoms in the semi-solid state.

Microstructure Evolution of AZ91D Magnesium Alloy Semi-solid Billets Prepared by a New SIMA Method

By using equal channel angular extrusion (ECAE) as strain induced step in strain induced melt activated (SIMA) and completing melt activated step by using semi-solid isothermal treatment, a new SIMA method is introduced firstly. The results show that semi-solid billet with highly spheroidal and homogeneous grains with the average grain size of 20μm can be prepared by new SIMA method. High mechanical properties, such as ultimate tensile strength of 321.8MPa and elongation of 15.2% are obtained in magazine plate components thixoforged using semi-solid billet prepared by new SIMA.

Application of equal channel angular extrusion to semi-solid processing of magnesium alloy

A new method called new strain induced and melt activated (new SIMA) is introduced firstly through using equal channel angular extrusion (ECAE) as strain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment, by which semi-solid billet with fine spheroidal grains with average grain size of 5 μm can be prepared. Comparing with common SIMA, semi-solid processed satellite angle frame components using semi-solid billet prepared by new SIMA have higher room temperature and 393 K high temperature mechanical properties.