不同镁含量Al-Si-Cu合金半固态加工的组织演变（英文）

采用传统铸造工艺制备了一系列Al-6Si-3Cu-(0.3-2)Mg合金。采用倾斜冷却法制备原料,然后在液相分数为50%时进行触变成形。研究镁含量对铸态和半固态条件下Al-Si-Cu合金显微组织的的影响。研究结果表明,在Al-Si-Cu合金中添加镁,形成Al_5Cu_2Mg_3Si_5和Mg_2Si相,消耗了部分Al_2Cu相和Si。添加Mg后,针状β-Al_5FeSi相转变成汉字状的π-Al8Mg3Fe Si6相。对于铸态合金,初生α(Al)为树枝晶,随着Mg含量的增加,树枝晶逐渐减少。此外,镁的添加可明显减小α(Al)晶粒,但对硅的形貌无明显影响。对于触变成形合金,合金的显微组织为细小的球状初生相,且均匀分布硅和碎片状的金属间化合物。共晶硅由薄片状和针状转变成细小纤维状粒子。镁对半固态加工合金的共晶硅作用明显。Mg_2Si初生粒子由多边形粒子转变成细小球状粒子,而汉字状π-Al_8Mg_3FeSi_6转变成紧凑结构。随着A319合金中Mg含量的增加,触变成形合金的硬度、屈服强度和抗拉强度均增加,而伸长率降低。

铜含量对触变成形Al-Si-Cu-Mg合金显微组织与力学性能的影响（英文）

研究了铜含量对触变Al-6Si-xCu-0.3Mg(x=3,4,5,6,质量分数,%)合金显微组织与力学性能的影响。试样在液相分数为50%时进行触变成形,并对部分样品进行T6热处理。采用光学显微镜、扫描电子显微镜、能谱仪和X射线衍射、硬度和拉伸测试对样品进行表征。结果表明,冷却倾斜板铸造和触变成形工艺能促进铝基体中细小分散的金属间化合物的形成。与硬模铸造相比,合金的力学性能大幅度提高。随着铜含量的增加,触变成形合金的硬度和拉伸强度提高。热处理触变成形Al-6Si-3Cu-0.3Mg合金的抗拉强度、屈服强度和伸长率分别为298MPa、201 MPa和4.5%。而当铜含量增加至6%时,合金的抗拉强度、屈服强度和伸长率分别为361 MPa、274 MPa和1.1%。触变成形Al-6Si-3Cu-0.3Mg合金的失效形式为韧窝断裂,而当铜含量增加至6%时,失效形式为解理断裂。

Cu和Mg对2014铝合金触变成形性和力学性能的影响（英文）

触变成形是使金属在半固态时发生变形的一种加工方法。该工艺的优点包括具有良好的表面光洁度,细小的显微组织和优越的力学性能,然而,该工艺主要是用铝铸件生产零件,没有充分利用其真正潜力。因此,可用热力学模拟进行合金成分设计。研究减少铜含量和增加硅、镁含量对2014铝合金触变成形的影响,包括模拟和实验验证两部分。结果表明,增加合金中硅含量和降低铜含量,可以降低合金的凝固区间温度,扩大特定液相分数之间的工作温度窗口,这对该工艺有利。高的固溶温度导致Mg2Si化合物的分解。Mg含量的增加导致致密π-Al8FeMg3Si6相的形成和尖片状结构β-Al5FeSi相的减少,提高合金的强度。后续T6热处理进一步提高改性合金的强度。

镁含量对触变成形A319合金显微组织演变和力学性能的影响（英文）

研究不同镁含量对触变成形A319合金显微组织和拉伸性能的影响。合金在含50%液相时进行触变成形,并对部分合金进行T6热处理。采用光学显微镜、扫描电子显微镜、能量散射谱、X射线衍射和拉伸试验对合金进行表征。结果表明,镁可以细化合金中共晶硅。当镁含量为1.0%和1.5%时,合金中形成致密的Al9Fe Mg3Si5相。随着镁含量的增加,触变成形合金的拉伸强度增加。热处理后的触变成形A319合金的抗拉强度、屈服强度和伸长率分别为298 MPa,201 MPa和4.5%。而对于添加1.5%Mg的触变成形A319合金,其热处理后的抗拉强度、屈服强度和伸长率分别为325 Pa、251 MPa和1.4%。触变成形A319合金表现为韧窝断裂,而添加1.5%Mg的A319合金表现为混合断裂,在合金表面可观察到韧窝断裂和解理断裂。

Microstructural Evolution of Solid-solution-treated Zn-22Al in the Semisolid State

The effect of solid-solution-treatment on the semisolid microstructure of Zn-22Al with developed dendrites was investigated. Forming Zn-22Al products by semisolid metal processing offers significant advantages, such as reductions in macro-segregation, porosity and forming costs. Thermal and rnicrostructural analyses of the formed Zn-22Al alloy were performed by differential scanning calorimetry, scanning electron microscopy and optical microscopy. The changes in the microstructures and phase transformation in response to various solid- solution-treatments were analysed. In this study, as-cast samples were held isothermally at 330 ℃ for 0.5- 5 h and then partially remelted at a semisolid temperature of 438 ℃ for 1 h to produce a solid-globular grain structure in a liquid matrix. A non-dendritic semisolid microstructure could not be obtained when the traditionally cast Zn 22Al alloy with developed dendrites was subjected directly to partial remelting. After solid-solution-treatment at 330 ℃, the black interdendritic eutectics were dissolved, and the dendritic structures gradually transformed into uniform β structures when the treatment time was increased. The coarsened and merged dendrites were separated as a result of penetration by the liquid phase and melting of the residual eutectic at sites along the former grain boundaries. The microstructure of the solid-solution- treated sample transformed into a small globular structure; the best shape factor of 0.9, corresponding to a particle size of 40 ± 16 μm, is achieved when the sample was treated for 3 h followed by direct partial remelting into its semisolid zone.

Microstructural evolution,dislocation density and tensile properties of Al–6.5Si–2.1Cu–0.35Mg alloy produced by different casting processes

Al–Si–Cu–Mg foundry alloys are used in casting process technologies.However,their strength properties remain low due to their microstructural characteristics and porosity.In this work,the microstructural characteristics,dislocation densities,and mechanical properties of Al–Si–Cu–Mg cast alloys prepared through different casting methods were studied experimentally.Four casting processes,namely,gravity casting(GC),rheocasting(RC),thixoforming(Thixo),and Thixo with heat treatment,were used.The GC and RC samples had mainly dendriticα-Al phase microstructures and exhibited coarse Si particles and intermetallic compounds in their interdendritic regions.By contrast,the Thixo and heat-treated Thixo(HT-Thixo)samples exhibited microstructural refinement with uniformly distributedα-Al globules,fine fibrous Si particles,and fragmented intermetallic compounds amongα-Al globules.The accumulation of dislocation densities increased in the Thixo sample as the strain was increased due to plastic deformation.Furthermore,the ultimate tensile strength and yield strength of the HT-Thixo sample increased by 87%and 63%,respectively,relative to those of the GC sample.The cleavage fracture displayed by the GC and RC samples led to brittle failure.Meanwhile,the Thixo and HT-Thixo samples presented dimple-based ductile fracture.