冷轧预变形对新型铝锂合金的时效析出与力学性能影响

采用大气熔炼铸造及热变形方法制备了Al-4.5Cu-1Li-0.7Mg-1Zn-0.3Ag-0.3Mn-0.2Zr新型铝锂合金板材。通过维氏硬度、拉伸性能、扫描电镜、透射电镜等方法，研究了固溶后不同冷轧预变形量对显微组织和力学性能影响。结果表明，时效前的冷轧预变形量有效促进了新型铝锂基体合金中T1(Al2CuLi)相的析出与均匀分布，减少了θ′(Al2Cu)相的体积分数。冷轧预变形量的增加，缩短了峰时效时间，晶界析出相由连续析出变为非连续析出，无沉淀析出区宽度变小。当冷轧预变形量为15%时，时效态合金的屈服强度与抗拉强度分别达到了668 MPa、690 MPa，延伸率保持在7.9%。     

铸态Ti-20Zr-20Al钛合金动态压缩力学性能与断裂机制研究

采用X射线衍射仪、金相显微镜、分离式霍普金森杆和扫描电镜等手段研究了Ti-20Zr-20Al钛合金在动态压缩条件下的微观结构、力学性能和断裂机制。结果表明,Ti-20Zr-20Al铸态合金由Zr基体相和TiAl/Ti₃Al针状相组成; 随着应变率增加,合金的抗压强度增加,失效应变显著增加; Ti-20Zr-20Al合金的断裂机制为解理断裂; 随着应变率增加,试验压缩断裂后碎片总数增大,平均粒径减小。采用DID模型模拟的材料碎片尺度与实验结果比较吻合,Grady模型与实验结果的偏差较大。     

TC4合金表面Cu/石墨复合镀层的摩擦磨损行为

采用无氰电镀工艺在TC4合金表面制备了Cu/石墨复合镀层，研究了镀层的组织结构和摩擦磨损行为。结果表明，采用无氰电镀方法能够在TC4合金表面制备出组织致密且与基体结合紧密的Cu/石墨复合镀层，但增加镀层中石墨的含量会降低镀层与基体合金的结合强度，并导致硬度小幅下降。摩擦磨损实验结果表明，Cu/石墨复合镀层具有优良的摩擦磨损防护性能，归因于石墨有效降低了镀层的摩擦系数和磨损率；对镀层磨损形貌、磨损产物和摩擦系数的综合分析结果表明，纯铜镀层的摩擦磨损机制主要为犁削磨损、黏着磨损和剥层磨损，Cu/石墨复合镀层的磨损机制为轻微的削层磨损和疲劳磨损。     

Microstructure and tensile properties of rapid-cooling friction-stir-welded AZ31B Mg alloy along thickness direction

Rapid-cooling friction-stir-welding (FSW) was used to join AZ31B magnesium alloy plates of 6 mm in thickness. The microstructure and mechanical properties in thickness direction were carefully investigated with electron backscattered diffractometer, and transmission electron microscope. The obtained results showed that ultrafine grains with high dislocation density were obtained in the top region of the weld due to liquid CO₂ cooling. A large number of twins and second-phase particles were also induced in these refined grains. The basal texture intensity was significantly reduced due to the appearance of twins. The top region showed the higher strength and elongation compared with the bottom region, and the welding efficiency reached 93%. This work provided a simple and efficient strategy for manufacturing a gradient structure in the FSW Mg alloy joint.     

Process and joint quality of ultrasonic vibration enhanced friction stir lap welding

In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects.     

汽车发动机用AZ91D合金的表面喷涂与性能

采用热喷涂工艺在压铸态AZ91D合金表面制备了Al涂层,研究了热处理温度和保温时间对AZ91/Al涂层界面组织形貌的影响,并对比分析了扩散层的耐腐蚀性能和耐磨性能。结果表明,热处理前Al涂层与基材为机械结合,热处理后Al涂层与AZ91合金基材的界面处可形成冶金结合扩散层,且随着保温时间延长,扩散层厚度不断增加;热处理温度在375 ℃以下时扩散层主要由β-Mg₁₇Al₁₂相构成,375 ℃×8 h热处理后为α-Mg+β-Mg₁₇Al₁₂相,425 ℃×1 h热处理后为γ-Mg₂Al₃和β-Mg₁₇Al₁₂相。AZ91合金基材和扩散层腐蚀电位从高至低顺序为γ>β>α+β>AZ91合金基材,扩散层的腐蚀电流密度均低于AZ91合金基材,阻抗谱图中容抗弧半径从大至小顺序为γ>β>α+β>AZ91合金基材,扩散层的耐腐蚀性能均优于AZ91合金基材;γ、β和α+β扩散层的摩擦稳定性系数都高于AZ91合金基材,而磨损速率和磨痕宽度都要小于AZ91合金基材,其中β扩散层的磨损速率和磨痕宽度最小,具有最佳的抵抗磨损的能力。     

自保护药芯焊丝明弧堆焊Fe-Cr-C-B-W合金的组织及性能

采用自保护药芯焊丝明弧堆焊技术制备五组不同钨含量的Fe-Cr-C-B-W合金. 借助金相显微镜、扫描电子显微镜、X射线衍射仪、洛氏硬度计和磨损试验机分析堆焊合金的组织及性能. 结果表明，合金的显微组织由马氏体、残余奥氏体、M₇(C,B)₃，M₃(C,B)，Fe₃W₃C和WC组成. 大部分钨元素被迁移到晶界生成了比WC稳定性更好的Fe₃W₃C缺碳复合相，堆焊层中没有典型的初生WC硬质相颗粒生成. 随着钨添加量的增多，共晶硬质相M₇(C,B)₃，M₃(C,B)和Fe₃W₃C随之增多，间距减小，呈连续网状均匀分布. 当钨的添加量为12%时，堆焊层的耐磨性达到最佳.     

Effect of microstructure on the fatigue crack growth behaviour of a near-α Ti alloy

Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure.     

Effect of microbial hydrogen consumption on the hydrogen permeation behaviour of AISI 4135 steel under cathodic protection

The feasibility of microbial hydrogen consumption to mitigate the hydrogen embrittlement (HE) under different cathodic potentials was evaluated using the Devanathan-Stachurski electrochemical test and the hydrogen permeation efficiency η. The hydrogen permeation efficiency η in the presence of strain GA-1 was lower than that in sterile medium. The cathodic potential inhibited the adherence of strain GA-1 to AISI 4135 steel surface, thereby reducing the hydrogen consumption of strain GA-1. The adherent GA-1 cells were capable of consuming ‘cathodic hydrogen’ and reducing the proportions of absorbed hydrogen, indicating that it is theoretically possible to control HE by hydrogen-consuming microbes.     

A dense and compact laser cladding layer with solid metallurgical bonding significantly improved corrosion resistance of Mg alloy for engineering applications

Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm² for Mg alloy to 13 μA/cm² for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications.