Densification process of 10%B_4C-AA2024 matrix composite strips by semi-solid powder rolling

Semi-solid powder rolling（SSPR） is a novel strip manufacturing process,which includes the features of semi-solid rolling and powder rolling.In this work,densification process and deformation mechanisms of B4 C and AA2024 mixed powders in the presence of liquid phase were investigated.The relationships between relative densities and rolling forces were analyzed as well.The results show that liquid fraction plays an important role in the densification process which can be divided into three stages.Rolling deformation is the main densification mechanism in deformation area when the liquid fraction is lower than 20%.When the liquid fraction is equal to or higher than 20%,the flowing and filling of liquid phase are the densification mechanisms in deformation area.The relative densities increase with increasing rolling forces.The relative density–rolling force curves are similar at 550 °C and 585 °C.The characteristics of the curve shapes are apparently different at 605 °C and 625 °C.

Effects of Cr and Cr/Mn Combined Additions on Semi-Solid Microstructures of Al-Mg-Si Alloys Produced by D-SSF Process

The effects of Cr and Cr/Mn combined additions on the semi-solid microstructure of wrought Al-Mg-Si alloys are investigated.In the Cr-added alloy,the Al-7Cr compound is formed with homogeneously distributed in theα-Al matrix after homogenization.Both of the Al-7Cr andα-Al-（12）Mn3-Si-2 dispersiod particles are found in the homogenized microstructure of the Cr/Mn-added alloy.In the semi-solid microstructures,the smallestα-Al grains are obtained in the 60% cold-rolled alloys.After prolonged holding time,theα-Al grain size of the Cr/Mn-added alloy is smaller than that of the Cr-added alloy.Heavy deformation by cold-rolling accelerates spheroidization of theα-Al grains.The D-SSF process is found to be useful to modify the microstructures of both the Cr-added and Cr/Mn-added Al-Mg-Si alloys.

Microstructural evolution during semisolid state strain induced melt activation process of aluminum 7075 alloy

The effects of compression ratio on the microstructure evolution of semisolid 7075 Al alloy produced by the strain induced melt activation （SIMA） process were investigated. The samples were cold deformed by compression into the different heights up to 40% reduction. The isothermal holding treatments were carried out at 625 ℃ for predetermined time intervals. The results reveal that the average grain size is gradually reduced with the increase of the compression ratio. When the compression ratio surpasses 30%, the above descending trend is not as evident as that below 30% reduction. During the subsequent heat treatments, the recrystallization is induced in the deformed samples by the increasingly accumulated strain energy. The grain growth mechanisms and the microstructural coarsening of the SIMA processed 7075 Al alloy were discussed and confirmed.

Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys

High-entropy alloys can be compelling raw materials for semi-solid applications.In the present study,the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi(x=0,1,2,3)alloys was investigated.Arc-melted samples were cross-rolled at room temperature and then isothermally treated at 1175℃in the semi-solid state for 300 s.Microstructural characterization showed that the alloys containing Cu were formed by two fcc phases.Notably,the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich phase.During solidification,this phase,which is the last to form,nucleates and epitaxially grows on the Cu-lean phase.All the studied CoCrCuFeNi alloys exhibited the same melting behavior.The Cu-rich phase melts at approximately 1120℃,whereas the Culean phase melts at approximately 1350℃,providing a suitable processing temperature range of more than 200℃.The semi-solid microstructures were considerably refined and globular regardless of the alloy composition,being suitable for semi-solid processing.Furthermore,each fcc phase exhibited roughly the same composition under the different processing conditions.The Cu content in the Cu-lean phase was approximately 10 at.%,while Co,Cr,Fe,and Ni were in an approximately equiatomic ratio.Meanwhile,the Cu content was between 80 at.%and 86 at.%in the Cu-rich phase.The isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature(1300℃)only caused the globules to coarsen.In conclusion,this work showed that these alloys can be potential candidates for semi-solid processing.

颗粒形貌及热处理对SiC_p/2024Al复合材料性能的影响

采用粉末半固态触变成形工艺制备了SiCp体积分数为60%的2024Al复合材料。研究了SiCp形貌及热处理对复合材料性能的影响。结果表明,经表面整形的SiCp制备的复合材料增强体颗粒均匀弥散地分布在铝基体上,其致密度能达到99.97%。对复合材料进行去应力退火和T6热处理后,复合材料得到最佳综合性能,其抗弯强度和硬度得到明显提高,与复合材料热处理前相比,分别提高了47.5%和57.7%。复合材料的断裂整体表现为SiCp的解理断裂,基体呈现出撕裂。对SiCp整形和复合材料退火及T6热处理后降低了复合材料的热膨胀系数,分别达到(4.85~8.51)×10^-6、(4.86~8.32)×10^-6℃^-1。经改进后的H-J模型可以更好地适用于混合增强和双峰粒径分布的情况。对SiCp整形和复合材料退火及T6热处理后显著提高了复合材料的热导率,分别达到195、206W·m^-1·K^-1。