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microstructure evolution of hot pressed AZ91D alloy chips reheated to semi-solid state

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Transactions of Nonferrous Metals Society of China 2012年第12期22卷 2906-2912页

作者：许红雨吉泽升胡茂良王振宇哈尔滨理工大学材料科学与工程学院哈尔滨150040

AZ91D magnesium alloy chips, which were directly collected on the spot of machining process, were recycled to prepare billet via hot pressing for semi-solid processing. The semi-solid microstructure evolution of the billet during reheating was investigated. The results indicate that there are three stages during reheating to semi-solid state: the dissolution of Mg17Al12 and diffusion of Al into α-Mg matrix, the melting of the region with high content of solute and formation of isolated solid particles, and spheroidization and growth of solid particles. Meanwhile, a number of entrapped liquid droplets form within solid particles. In addition, the number and size of entrapped liquid droplets rely on the holding time in the semi-solid temperature range. With increasing isothermal holding time, the solid fraction remains unchanged when the solid-liquid system reaches the dynamic equilibrium at last, while the solid particles become more globular and the average size of solid particles increases owing to the decreasing of interfacial energy and the effect of interfacial tension.

关键词： AZ91D alloy chips semi-solid microstructure microstructure evolution recycling entrapped liquid droplet interfacial energy interfacial tension

Effects of Extrusion Processing on microstructure of 7075Al Alloy in the semi-solid State

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Journal of Wuhan University of Technology(Materials Science) 2019年第6期34卷 1433-1443页

作者： SONG Yang ZHANG Zhiming WANG Kai LI Hongxu ZHU Zizong Department of Materials Science and Engineering Chongqing UniversityChongqing 400030China

A recrystallization and partial melting(RAP) process was introduced to prepare the semi-solid 7075 aluminum alloy used for thixoforming. In order to obtain an ideal semi-solid microstructure, a series of extrusion experiments were conducted to comparatively investigate the optimum extrusion process parameters. Commercial 7075 Al alloy samples were firstly extruded with varying extrusion ratios below the recrystallization temperature followed by homogenization, then these samples were reheated to the semi-solid state and held in the range of 5 to 50 minutes. The experimental results show that varying process cause the difference in the deformation degree and microstructure for as-extruded samples, resulting in various semi-solid microstructure. It is verified that the formation of equiaxed grains in semi-solid microstructure depends on recrystallization behavior of extruded samples during partial melting. Both relative high extrusion temperature and low extrusion ratio lead to high volume fraction of recrystallized area, thus entirely equiaxed solid grains in semi-solid 7075 Al alloy samples can be obtained finally. In addition, Ostwald ripening was determined as the dominate coarsening mechanism of solid grains in semi-solid state for this 7075 Al alloy during the RAP route. The influence of predeformation on recrystallization behavior of this 7075 Al alloy was discussed in detail.

关键词： aluminum alloys extrusion process recrystallization and partial melting(RAP) semi-solid microstructure coarsening mechanism

microstructures and mechanical properties of semi-solid squeeze casting ZL104 connecting rod

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Transactions of Nonferrous Metals Society of China 2018年第2期28卷 235-243页

作者：王永飞赵升吨张晨阳西安交通大学机械工程学院西安710049

semi-solid squeeze casting（SSSC） and liquid squeeze casting（LSC） processes were used to fabricate a ZL104 connecting rod, and the influences of the process parameters on the microstructures and mechanical properties were investigated. Results showed that the tensile strength and elongation of the SSSC-fabricated rod were improved by 22% and 17%, respectively, compared with those of the LSC-fabricated rod. For SSSC, the average particle size（APS） and the shape factor（SF） increased with the increase of re-melting temperature（Tr）, whereas the tensile strength and elongation increased first and then decreased. The APS increased with increasing the mold temperature（Tm）, whereas the SF increased initially and then decreased, which caused the tensile strength and elongation to increase initially and then decrease. The APS decreased and the SF increased as squeezing pressure（ps） increased, and the mechanical properties were enhanced. Moreover, the optimal Tr, ps and Tm are 848 K, 100 MPa and 523 K, respectively.

关键词： aluminum alloy semi-solid squeeze casting semi-solid microstructure tensile strength elongation connecting rod

Effect of ECAP process on liquid distribution of AZ80M alloy during semi-solid isothermal heat treatment

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Transactions of Nonferrous Metals Society of China 2021年第6期31卷 1599-1611页

作者： Ling-ling FAN Ming-yang ZHOU Yang-yang GUO Yu-wen-xi ZHANG Gao-feng QUAN Key Laboratory of Advanced Technologies of Materials Ministry of EducationSchool of Materials Science and EngineeringSouthwest Jiaotong UniversityChengdu 610031China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of ChinaChengdu 610213China

Two kinds of semi-solid samples of AZ80−0.2Y−0.15Ca(wt.%)(AZ80M)magnesium alloy were prepared by semi-solid isothermal heat treatment of materials with and without equal channel angular pressing(ECAP)*** microstructures of initial and semi-solid treated samples were compared and *** results showed a significant difference in the liquid phase distribution between three-pass ECAP processed(3P)and as-received samples during the isothermal heating *** semi-solid 3P sample showed a more uniform liquid distribution due to its smaller dihedral ***,the coarsening processes of solid grains of as-received and 3P samples were dominated by the coalescence and Ostwald ripening mechanism,*** difference of coarsening processes was mainly related to the proportion of the high-angle grain boundaries in materials,which further affected the evolution behavior of the liquid pools.

关键词： AZ80M equal channel angular pressing semi-solid microstructure liquid phase distribution coarsening mechanism

Microstructural evolution of fine-grained ZA27 alloy during partial remelting

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China Foundry 2010年第4期7卷 331-336页

作者： Chen Tijun Fu Mingfeng Hao Yuan Key Laboratory of Gansu Advanced Nonferrous Materials Lanzhou University of Technology Lanzhou 730050 China

The microstructural evolution process of fined-grained ZA27 alloy during partial remelting has been investigated. The relationship between the as-cast and semi-solid microstructures has been discussed in particular. The results indicate that a semi-solid microstructure with small and spheroidal primary particles can be obtained when the ZA27 alloy is partially remelted. The microstructural evolution can be divided into four stages, the initial coarsening of the dendrites due to coalescence of dendrite arms, structural separation resulted from the melting of residual interdendritic eutectic, spheroidization due to the partial melting of solid particles and final coarsening attributed to the coalescence and Ostwald ripening. An equiaxed dendrite in the as-cast microstructure may evolve into one spheroidal particle in the semi-solid microsturucture after being partially remelted. The more equiaxed the dendrites in an as-cast microstructure are, the more spheroidal the solid particles in the semi-solid microstructure will be. Finer primary particles could be obtained if the alloy with finer as-cast microstructure was partially remelted. However, due to the coalescence effect, their sizes cannot be reduced further if the refined as-cast microstructure reached a certain extent.

关键词： ZA27 alloy thixoforming semi-solid microstructure partial remelting

microstructure evolution of an Mg-Zn-Nd-Zr magnesium alloy during recrystallization and partial remelting process

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China Foundry 2013年第4期10卷 244-247页

作者： Tao Jianquan Wan Yuanyuan Sun Changjian Su Zhiquan Deng Tianquan Huang Jing No.59 Institute of China Ordnance Industry

To obtain a spheroidal microstructure of a semi-solid Mg-Zn-Nd-Zr alloy,which is favorable for the subsequent thixocasting process,the recrystallization and partial remelting(RAP)method was used in this study,and the microstructure evolution of the alloy and the mechanism of the shape factor change during the RAP process were *** as-cast Mg-Zn-Nd-Zr alloy was prepared in a metal mold and then extruded into bars with an extrusion ratio of 16:*** remelting was carried out on the extruded samples at 589℃(at a heating rate of 0.5℃·s-1)for different holding times ranging from 0 to 90 *** examine the effect of heating rate,partial remelting of samples at the heating rate of 2℃·s-1was also *** show that the extruded microstructure rapidly evolutes into recrystallized grains in the semi-solid state;the liquid f ilm initially forms at grain boundaries during the partial remelting,and then gradually changes from continuous into discontinuous state with the increase of holding time;this results in the agglomeration of adjacent grains and the decrease in shape *** value of shape factor increases continuously with holding time at f irst and reaches the maximum 0.62 when holding for 60 min,while decreases rapidly after a prolonged holding ***,local melting,mainly due to the inhomogeneous deformation during extrusion,becomes more signif icant and less uniformly distributed at a relatively higher reheating *** Mg-Zn-Nd-Zr magnesium alloy components have been thixo-cast successfully using the RAP method,which strongly proves the feasibility of RAP process in Mg-Zn-Nd-Zr alloy.

关键词： semi-solid microstructure extrusion partial remelting magnesium alloy