Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Annealed 7B04 Al sheets in thickness of 2 mm were subjected to friction stir welding (FSW) under three rotation rate and welding speed parameters of 1600 r/min, 200 mm/min; 800 r/min, 200 mm/min and 400 r/min, 400 mm/min, respectively. The effect of welding parameters on the tensile property and microstructure of the FSW joints were investigated, with more efforts focusing on the low-temperature superplasticity of the nugget zones (NZs). The results showed that FSW joints with high quality could be produced by controlling welding parameters, with a joint strength coefficient of 100% being obtained. Dynamic recrystallization took place in the NZs with fine and equiaxed grains generated. The grain size of the base material was about 300 μm, while it was significantly decreased in the NZs with decreasing the rotation rate: about 2, 1 and 0.6 μm for the above three samples, respectively. The fine grain structure of the NZs could facilitate their superplastic deformation. The NZs exhibited superplastic elongations ranged from 160% to 590% at 300 ℃ at strain rates of 1×10-3 and 3×10-4 s-1. The maximum superplasticity of 790% was obtained at 350 ℃ at the strain rate of 1×10-3 s-1. The ability to superplastic deformation disappeared in the NZs at 400 ℃.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： In this work, the hot rolling process of SiCp/2009Al composites is simulated using the fully coupled thermal-stress analysis in Abaqus/Explicit. By the investigation of formation process for rolling along with different fields of temperature, strain rate, strain and stress and their evolutionary history, the hot rolling mechanisms under complicated stress states is achieved. The results show that the maximum principal stress changes from compressive stress to tensile stress at the stage of rolling entrance and a reverse trend replaces it at the exit, and that the compressive stress is dominant in the deformation zone at the steady rolling stage. The temperature drop effect due to heat transfer is far greater than the temperature rise effect due to friction on the plate surface while the temperature rise is embodied in the center due to plastic deformation. Besides, the effect of strain rate on flow stress plays a leading role at the entrance and exit stage, and the flow stress on the plate surface in the deformation region is mainly determined by strain and temperature except the stick zone which is controlled by strain rate, however, the center flow stress in deformation is mainly affected by temperature.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： By using high energy ball- milling and vacuum hot-pressed sintering techniques, ultrafine grained carbide cement WC-2.5TiC-10Co were prepared, and the effect of grain growth inhibitors Cr3C2, VC, TaC and NbC on microstructures and mechanical properties were studied by X- ray diffractometer, field emission scanning electron microscope (FESEM) and mechanical performance test. The results indicates that the particle size of the WC powder can be reduced to less than 0.2 mm from 0.6 mm after 30 h of high energy ball-milling at a rotation speed of 350 r/min and ball/powder ratio of 10: 1. After vacuum hot-pressed sintering at 1410℃ for 1h, no new reactive product formed revealed by XRD. When 0.45 % Cr3C2, 0.3 %VC, 0.5 %TaC or NbC were added to the carbide cement, a small quantity of abnormally coarsened WC grains occurred, while the fractured surfaces display loose and smooth. Analyzing the fractured surfaces indicate that cleavage cracking in coarsened WC grains was caused by concentrated stress and become the source of materials fracture. When the contents of inhibitors Cr3C2 and VC were both more increased 0.1%, the grain size of WC can be reduced less than 0.5 mm. In such a case, the fractured surfaces are intimate and step-like, while the bending strength can be increased by 20%. Inhibitors TaC and NbC have not pronounced effect on the preventing the WC grain growth, while the addition of NbC is most effective in improving the relative density of the carbide cement.
Subjects: Materials Science >> Materials Science (General) submitted time 2017-04-10 Cooperative journals: 《金属学报》
Abstract：采用粉末冶金法制备了名义尺寸150、300、500 μm的片层石墨增强铝基（50vol.%Gf/Al）复合材料，得到密度均接近理论密度的致密复合材料坯锭。片层石墨与铝合金基体结合紧密，界面处无裂纹、孔洞等缺陷。片层石墨的xy方向基本与坯锭的xy方向平行，但受粉末冶金工艺的影响，较小片层石墨的xy方向与坯锭的xy方向略有偏差，随着片层石墨的尺寸增大，偏差逐渐减少。复合材料的强度随着片层石墨尺寸增加逐渐降低。150 μm片层石墨复合材料的弯曲强度为82 MPa，当片层石墨尺寸增至500 μm时，强度降低至39 MPa。片层石墨强度较低，裂纹容易沿片层石墨的层间扩展，随着片层石墨尺寸增大，这一现象更加明显，容易在断口中观察到片层石墨剥离的现象。复合材料xy方向的热导率随片层石墨尺寸增大而增加，最高可达604 W/m ? K，与尺寸较小的片层石墨相比提高63%。300、500 μm片层石墨复合材料的界面换热系数略低于理论值，但150 μm片层石墨复合材料的界面换热系数明显小于理论值。除了片层石墨的尺寸，其形状、分布和内部缺陷等对复合材料的热导率也有一定的影响。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：在三组参数下（1600-200、800-200、400-400，转速（rpm）-焊速（mm/min））对2 mm厚的退火态7B04铝合金薄板进行搅拌摩擦焊接，研究了焊接参数对焊缝质量及微观组织的影响，并分析了焊核区的低温超塑性变形行为。结果表明，通过控制焊接参数，可获得良好的焊接质量，接头强度系数达100%。焊核区发生动态再结晶，生成细小等轴晶，且晶粒尺寸随转速的降低而显著减小（母材晶粒尺寸为~300 μm，1600 rpm下为2 μm，800 rpm 下为1 μm，400 rpm下为 0.6 μm）。这种细晶组织有利于焊核区超塑变形，在300 oC，焊核区在1×10-3 s-1、3×10-4 s-1下获得了160~590%的延伸率，在350 oC、1×10-3 s-1条件下获得高达790%的最大延伸率，在～400oC时超塑性变形行为消失。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：本文结合本研究组的研究结果，简述了异种材料、高熔点材料、铝基复合材料的焊接，以及温度场模拟、复合材料/超细晶材料制备等搅拌摩擦焊接与加工领域几个热点问题的研究进展。分别对影响异种金属材料焊接的关键因素与界面结合机理，高熔点材料（钢、钛合金）焊接过程中的组织演变及焊接工具的发展，铝基复合材料接头组织性能与工具磨损，温度场热源模型及温度场的影响因素与变化规律，搅拌摩擦加工复合材料及超细晶材料的组织特点及性能等内容进行了总结与评述。同时，对未来相关领域的研究方向进行了展望。
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