Investigation on the plastic work-heat conversion coefficient of 7075-T651 aluminum alloy during an impact process based on infrared temperature measurement technology

The plastic work-heat conversion coefficient is one key parameter for studying the work-heat conversion under dynamic deformation of materials. To explore this coefficient of 7075-T651 aluminum alloy under dynamic compression, dynamic compression experiments using the Hopkinson bar under four groups of strain rates were conducted, and the temperature signals were measured by constructing a transient infrared temperature measurement system. According to stress versus strain data as well as the corresponding temperature data obtained through the experiments, the influences of the strain and the strain rate on the coefficient of plastic work converted to heat were analyzed.The experimental results show that the coefficient of plastic work converted to heat of 7075-T651 aluminum alloy is not a constant at the range of 0.85–1 and is closely related to the strain and the strain rate. The change of internal structure of material under high strain rate reduces its energy storage capacity, and makes almost all plastic work convert into heat.

搅拌摩擦焊AA7075-T651铝合金厚板的显微组织和力学性能（英文）

研究厚度为10和16 mm AA7075-T651板的搅拌摩擦焊接过程。通过仔细选择焊接过程参数可获得无缺陷、全渗透焊接样品。两种焊接接头都出现极细的再结晶粒,而10 mm厚板焊接接头的晶粒组织更细。试样的显微组织观察结果表明,焊件热影响区的硬度显著降低。16 mm厚合金板焊接接头的硬度降低较大。与16 mm厚合金板相比,10 mm厚合金板焊件具有较优的拉伸性能。在拉伸实验过程中,两种厚度的合金板焊件均在热影响区发生断裂。样品的TEM结果表明,热影响区由沿晶界的宽化无沉积区和晶体内沉淀的部分溶解组成。因此,采用搅拌摩擦焊在AA7075-T651上可制得单道次无缺陷焊件,且10 mm厚合金板焊件表现出较高的焊接效率。

Texture and mechanical properties of metal inert gas welded 6082-T651 aluminum alloy joints

Metal inert gas(MIG)welding was conducted with 12 mm thick 6082-T651 aluminum alloy plate to investigate the microstructure and mechanical properties of welded joint.The microstructure and element distribution of weld seam were characterized by electron backscattered diffraction(EBSD)and electron probe microanalysis(EPMA).The weld seam has typical cube texture({001}<100>)characteristics.The closer to the center of weld seam,the weaker the texture feature,the higher the proportion of high-angle grain boundaries.The average tensile strength of joint was 232 MPa which is up to 72%of 6082 aluminum alloy base metal,and the bending angle for the root bend test sample reached 90°without cracks.The lack of strengthening phase and the existence of welding pores and inclusions in the weld seam caused the degradation of mechanical properties of resultant joint.The microhardness increased from the weld center to the base metal,but the overaging zone caused by welding thermal cycle was softening part of the joint,which had lower hardness than the weld seam.

应力控制模式下疲劳损伤对AA7075-T651铝合金腐蚀行为影响的研究

通过AA7075-T651铝合金中断疲劳实验、含疲劳损伤试样的拉伸实验、电化学实验及微观结构观察等系统地探究了应力控制模式下疲劳损伤对其力学性能及腐蚀行为的影响。实验结果表明:应力控制模式下的疲劳损伤不仅可以提升AA7075铝合金的综合力学性能,还可以增加其耐腐蚀性,而疲劳损伤前后的微观结构变化(位错密度增加及二次相析出)是影响AA7075铝合金力学性能及腐蚀行为变化的根本原因。

Friction Stir Welding of Dissimilar Aluminum Alloys

Dissimilar aluminum alloys AA2024-T365 and AA5083-H111 were welded by friction stir process. Welding parameters such as tool rotational speed (900, 1120 and 1400 rpm), weld speeds (16, 40 and 80 mm/min) and tool pin profiles (square, triangular and stepped) were used to weld many joints to study their effect on the mechanical properties of the joint. Also, different locations of the material were studied as other parameter. The mechanical properties were evaluated using tensile and hardness tests. The microstructure characterization of the processed alloys was carried out using optical microscopy. Macro and microstructures of parent and welded specimens indicated that the weld parameters have a significant effect on mechanical and microstructural properties of the welds. However, defect-free as well as higher strength was obtained at higher speed of 80 mm/min.

腐蚀损伤对AA7075-T651铝合金疲劳行为影响的研究

为研究腐蚀损伤对AA7075-T651铝合金疲劳行为的影响,首先分别将AA7075-T651铝合金试样浸泡在3.5%(质量分数) NaCl溶液中150和500 h,然后,使用含腐蚀损伤试样进行疲劳试验,获得含不同腐蚀损伤特征试样的疲劳寿命分布特征。结果表明,与原始试样的疲劳寿命相比,相同载荷条件下腐蚀损伤会明显地降低铝合金的疲劳寿命,但是,尽管浸泡500 h试样的腐蚀损伤特征尺寸明显大于浸泡150 h的,两者的疲劳寿命差异却并不明显。针对腐蚀损伤特征与疲劳寿命的关系,本文采用缺口系数相关的Stromeyer三参数S-N预测模型,对含腐蚀损伤铝合金试样的疲劳寿命进行了预测分析,实验结果基本分布在预测结果的二倍分散带内,有效地验证了该寿命预测方法的准确性。

Effect of Temperature on Material Transfer Behavior at Different Stages of Friction Stir Welded 7075-T6 Aluminum Alloy

In this work, the morphologies of weld of 7075-T6 aluminum alloy via friction stir welding （FSW） were analyzed by optical microscopy, the temperature field was attained by numerical simulation, and the effect of temperature on material transfer behavior in the thermal-mechanical affected zone （TMAZ） at different stages was mainly investigated. The FSW process consists of three stages. It is very interesting to find that the maximum transfer displacement of material appears at the final stage of welding process, then at the stable stage and at the initial stage, which results from the difference of peak temperatures at different stages. At any stage, the material in TMAZ near the surface of weld transfers downwards, the material in the middle of weld moves upwards and the material near the bottom of weld hardly moves. In any cross section of weld, the largest transfer displacement of material appears in the middle of weld. The increase of rotational velocity and the decrease of welding speed are both beneficial to the transfer displacement of material in the middle of weld.