Al-4.1Cu-1.4Mg合金均匀化退火工艺研究

半连续水冷铸造的Al-4.1Cu-1.4Mg合金出现枝晶偏析。采用光学显微镜、扫描电镜、差热分析等手段研究工业化生产条件下合适的均匀化退火制度。研究结果表明:适宜于工业化生产的均匀化退火制度为(490±5)℃20 h。按该制度均匀化退火后Al-4.1Cu-1.4Mg合金枝晶偏析消除,弥散相分布也趋于均匀,铸造应力下降,加工性能良好。

微量Li、Zn对Al-4.2Cu-1.4Mg合金疲劳性能与微观组织的影响

通过断裂韧性测试、疲劳裂纹扩展速率测试、金相分析、透射电子显微分析(TEM)等研究了微量Li、Zn对Al-4.2Cu-1.4Mg合金疲劳裂纹扩展速率与微观组织的影响。结果表明,共同添加Li、Zn时能明显提高合金Al-4.2Cu-1.4Mg的断裂韧性,并降低合金的疲劳裂纹扩展速率。当同时添加少量Li和Zn时,少量Li和Zn的共同作用能使合金中的过剩相和弥散相数量、尺寸减小,分布趋向均匀。这是影响该合金疲劳性能和断裂韧性的微观机理。

Effects of La-Ce addition on microstructure and mechanical properties of Al-18Si-4Cu-0.5Mg alloy

The microstructural evolution and mechanical properties of Al-18 Si-4 Cu-0.5 Mg alloy modified by the addition of La-Ce rare earth elements through OM,SEM,EPMA and tensile tests were investigated.The results of OM and SEM analyses indicated that primary Si particles were significantly refined from coarse block-like and irregular polygonal shapes into fine flaky shapes,while eutectic Si particles were modified from coarse and needle-like into fine and rod-or coral-like shapes with increase of La-Ce addition.The alloy exhibited the minimum primary Si particle size and the best mechanical properties with the addition of 0.3 wt.%La-Ce.The average particle size decreased from 61 to 28 μm,the ultimate tensile strength increased from 222 to 242 MPa and the elongation increased from 3.2% to 6.3%.In addition,modification mechanisms and fracture modes were explored by the means of SEM and EPMA.

Finite element analysis of stress-strain localization and distribution in Al-4.5Cu-2Mg alloy

Finite element analysis has been carried out to understand the effect of various processing routes and condition on the microscale deformation behavior of Al–4.5 Cu–2 Mg alloy. The alloy has been developed through four different routes and condition, i.e. conventional gravity casting with and without refiner, rheocasting and SIMA process. The optical microstructures of the alloy have been used to develop representative volume elements（RVEs）. Two different boundary conditions have been employed to simulate the deformation behavior of the alloy under uniaxial loading. Finally, the simulated stress-strain behavior of the alloy is compared with the experimental result. It is found that the microstructural morphology has a significant impact on stress and strain distribution and load carrying capacity. The eutectic phase always carries a higher load than the α（Al） phase. The globular α（Al） grains with thinner and uniformly distributed eutectic network provide a better stress and strain distribution. Owing to this, SIMA processed alloy has better stress and strain distribution than other processes. Finally, the simulated yield strength of the alloy is verified by experiment and they have great agreement.

Influence of Li addition on mechanical property and aging precipitation behavior of A1-3.5Cu-1.5Mg alloy

The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.

微量Zn对Al-4.2Cu-1.4Mg合金应力腐蚀与微观组织的影响

通过慢应变速率拉伸、动电位极化曲线测试、透射电子显微分析(TEM)、背散射电子衍射(EBSD)等实验较系统地研究了微量Zn对Al-4.2Cu-1.4Mg合金应力腐蚀与微观组织的影响规律。结果表明,微量Zn的添加显著影响合金的腐蚀性能,且随着Zn含量增加,合金的抗应力腐蚀敏感性以及其对应的开路电位均呈峰值变化,含Zn量0.29%合金的抗腐蚀能力最佳。EBSD研究表明,含0.29%Zn的Al-4.2Cu-1.4Mg合金与其它合金相比存在较多的低能量小角度晶界,这可能是微量Zn显著影响该合金抗应力腐蚀性能的主要原因。