Improvement in the mechanical properties of Al/SiC nanocomposites fabricated by severe plastic deformation and friction stir processing

Severely deformed aluminum sheets were processed by friction stir processing(FSP) with Si C nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone(HAZ).In the case of using a simple probe and the same rotational direction(RD) of the FSP tool between passes,at least three FSP passes were required to obtain the appropriate distribution of nanoparticles.However,after three FSP passes,fracture occurred outward from the stir zone during transverse tensile tests;thus,the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ.To improve the mechanical properties of the HAZ,we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP passes.The results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of Si C nanoparticles after two FSP passes.In these cases,fracture occurred at the HAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple probe.The fracture behaviors of the processed specimens are discussed in detail.

热输入对搅拌摩擦焊AA3003-H18板材显微组织和力学性能的影响（英文）

通过优化焊接参数,采用搅拌摩擦焊对不可热处理强化A3003-H18合金进行焊接以获得合适的接头。通过改变转速（800-1200 r/min）和行进速度（40-100 mm/min）比（ω/υ）,研究热输入对焊接样品显微组织和力学性能的影响。结果表明,随着转速提高,热输入增加,晶粒增长速度大幅增加,而随着行进速度提高,热输入增加,但晶粒增长速度略有增加。与低转速相比,高转速会降低搅拌区的硬度。而不同焊接参数对接头的拉伸强度的影响不明显。在低行进速度时,拉伸样品的断裂位置在前进侧的热影响区（HAZ）;而在高行进速度时,断裂位置在后退侧的HAZ/TMAZ界面。

非等温退火对大变形铝试样组织和力学性能的影响:模拟与实验（英文）

为了研究铝在非等温退火过程中的组织演变和流动应力,分别采用2、4和6道次多向锻造工艺,使试样应变量为1、2和3。然后,在150、200、250、300和350℃下对试样进行非等温退火。通过对变形阶段和退火阶段的模拟,研究位错密度和流动应力的演化规律。结果发现,经2、4和6道次多向锻造的试样在温度分别达到250、250和300℃时其热稳定性仍然较好。模拟结果与实验数据吻合较好。与模拟得到的流动应力值相比,经2道次和4道次多向锻造的样品在350℃非等温退火后的实验流动应力值偏低。其根本原因在于,模拟所用非等温退火模型仅是基于晶内位错密度演化,只考虑了回复和再结晶现象;然而,在350℃退火后,除了回复和再结晶外,还会发生晶粒长大现象,这使得模拟和实验得到的流动应力值出现偏差。

搅拌摩擦焊接Al-Cu双层复合板(英文)

对冷轧Al-Cu双层复合板进行搅拌摩擦焊接,获得了无缺陷的焊接接头。对搅拌摩擦焊过程中的金属流动行为和两层之间的混合进行了研究,考察了显微组织和硬度的变化。结果表明,在搅拌区的金属流动导致了在Cu层中前进侧生成条带状结构,在这些条带状结构中的细晶区域中,存在微量的Al颗粒和Al-Cu金属间化合物,这导致了其硬度的增加。

Microstructural evolution during ultra-rapid annealing of severely deformed low-carbon steel: strain, temperature, and heating rate effects

An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.

Microstructure and Mechanical Properties in Dissimilar Butt Friction Stir Welding of Severely Plastic Deformed Aluminum AA 1050 and Commercially Pure Copper Sheets

In this study,AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were used.The technique used for imposing the severe strain to the sheets was constrained groove pressing（CGP） process.The annealed and severely plastic deformed sheets were subjected to friction stir welding（FSW） at different rotation and traverse speeds.Cu was placed in advancing side.Constant offset of approximately 1 mm was used toward Al side for all welds.A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was found.For the FSWed CGPed samples,it was observed that the welding heat input caused grain growth and decrease in hardness value at Al side of the stir zone.It was found that,generally the weakest parts of weld joints of annealed and CGPed samples were Al base metal and stir zone,respectively.Further investigations showed that several forms of intermetallic compounds were produced.