定向凝固Al−6%Cu−5%Ni合金的显微组织特征和力学、电化学行为

在Al−6%Cu合金中添加5.0%Ni(质量分数),研究其对合金凝固时的冷却速率(T)和生长速率(V_(L)),显微组织中枝晶长度、金属间化合物(IMCs)的形貌和分布,以及最终性能的影响。研究在大冷却速率范围内制备的定向凝固Al−6%Cu−5.0%Ni合金铸锭沿长度方向的耐腐蚀性和拉伸性能。推导出一次枝晶间距(λ_(1))和二次枝晶间距(λ_(2))随T和V_(L)的演变规律。采用Hall−Petch公式计算沿铸件长度方向的断后伸长率(δ)和极限抗拉强度(σ_(U))与λ_(1)^(−1/2)的关系。在合金成分中添加Ni的强化效果优于细化枝晶组织的强化效果。在较高T下凝固的样品中形成细小的IMCs,且均匀分布在枝晶间,这种典型的显微组织使样品具有最高的耐腐蚀性。

Corrosion behavior of hypoeutectic Al-Cu alloys in H_2SO_4 and NaCl solutions

The aim of this work was to evaluate the electrochemical behaviour of hypoeutectic Al-Cu alloys immersed in two different solutions containing sulphate and chloride ions, respectively. The influence of Al2Cu associated to the dendritic arm spacing on the general corrosion resistance of such alloys is analysed. The typical microstructural pattern was examined by using scanning electron microscope. The corrosion tests were performed in both 0.5 M sulphuric acid and 0.5 M NaCl solutions at 25℃ by using an electrochemical impedance spectroscopy （EIS） technique and potentiodynamic polarization curves. Equivalent circuits by using the ZView software, were also used to provide quantitative support for the discussions. It was found that as the Cu content increased （i.e., increasing the Al2Cu fraction）, a higher susceptibility to the corrosion action in the NaCl solution is detected. In contrast, the tests carried out in the H2SO4 solution resulted in similar corrosion,rates for the three different hypoeutectic alloys.

通过凝固冷却速率调整Zn-1Mg-(0.5Mn,0.5Ca)合金的显微组织和显微硬度

生物可降解锌基合金,特别是添加合金元素的锌-镁(Zn-Mg)合金,已获得广泛研究以改善其力学性能和腐蚀性能。由于这些性能主要依赖于合金的显微组织,因此任何评价都应该从了解影响其形成的条件开始。本研究旨在探讨凝固冷却速率对Zn-1Mg-(0.5Ca, 0.5Mn)(质量分数,%)合金瞬态凝固过程中显微组织演化的影响。结果表明,两种合金的显微组织均含有3种相:η-Zn枝晶基体、Zn11Mg2金属间化合物和低共熔混合物中的Zn2Mg。MnZn9和两种含Ca相(CaZn11和CaZn13)分别与Mn和Ca的添加有关。与Zn-1Mg(质量分数,%)合金相比,添加Mn和Ca元素可以细化枝晶基体和低共熔混合物。建立冷却速率、枝晶间距或共晶间距之间的关系,从而提出实验生长规律。此外,为了研究添加Ca和Mn的效果,进行硬度测试。维氏显微硬度与二次枝晶间距之间的实验相关性表明,与二元合金相比,显微组织细化和典型的Ca、Mn基金属间化合物是导致硬度增加的主要原因。

Microstructural Morphologies and Experimental Growth Laws during Solidification of Monotectic and Hypermonotectic Al-Pb Alloys

AI-Pb alloys with monotectic and hypermonotectic compositions were directionally solidified under unsteady- state heat flow conditions. The cooling curves recorded during solidification allowed solidification thermal parameters such as the cooling rate （T）, growth rate （v） and thermal gradient （G） to be experimentally determined. Different microstructural patterns have been associated with the alloy solute content, i.e., AI-1.2 and 2.1 wt% Pb. A sequence of morphologies from the bottom to the top of the A1-1.2 wt% Pb alloy casting （monotectic） can be observed： Pb-rich droplets in the aluminum-rich matrix, followed by a region of microstructural transition formed by droplets and fibers and finally by a mixture of fibers and strings of pearls. A completely fibrous structure （without transition） has been observed along the entire AI-2.1 wt% Pb alloy casting （hypermonotectic）. The interphase spacing （λ） was measured along the casting length, and experimental correlations between λand experimental solidification thermal parameters have been established. Power laws with a -2.2 exponent expressing λ as a function of the growth rate, v, were found to better represent the fibrous growth of both AI-Pb alloys. Moreover, a single experimental law expressing λ as a function of both G and v was found to describe the fibrous growth of both the monotectic and the hypermonotectic alloys experimentally examined.

Horizontally Solidified Al-3 wt%Cu-(0.5 wt%Mg)Alloys:Tailoring Thermal Parameters,Microstructure,Microhardness,and Corrosion Behavior

In the present experimental investigation,Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(GR),cooling rate(CR),secondary dendrite arm spacing(λ2),Vickers microhardness(HV),and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures,that is,h-Al2Cu,S–Al2CuMg,and x-Al7Cu2 Fe,are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software,optical microscopy,and scanning electron microscopy/energy-dispersive spectroscopy.Moreover,electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings.Hall–Petch-type equations are proposed to represent the HV dependence onλ2.It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV;however,the Al–Cu binary alloy is shown to have lower corrosion current density(icorr)as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.

Dendritic Growth, Eutectic Features and Their Effects on Hardness of a Ternary Sn–Zn–Cu Solder Alloy

The present investigation is based on the results of a directionally solidified （DS） Sn-9 wt%Zn-2 wt%Cu alloy, including primary/secondary/tertiary dendrite arm spacings of the Sn-rich matrix, the morphologies of the eutectic mixture and the corresponding interphase spacing, the nature and proportion of the Cu-Zn intermetallic compound （IMC）. The main purpose is to establish interrelations of these microstructure features with experimental solidification thermal parameters, such as cooling rates and growth rates （v）, macrosegregation and hardness. Such interrelations are interesting for both industry and academy since they represent a tool permitting the preprogramming of final properties based on the design of the microstructure. In the case of Sn-Zn-Cu alloys, hardly anything is known about the combined effects of the length scale of the microstructure and fraction and distribution of the primary IMC on hardness. The alloy microstructure is composed of a β-Sn dendritic region, surrounded by a eutectic mixture of α-Zn and β-Sn phases and the γ-Cu5Zn8 IMC. The eutectic interphase spacing varies in the range 1.2-3.6 μm, with the α-Zn phase having a globular morphology for ν 〉 0.5 mm/s and a needle-like morphology for ν 〈 0.3 mm/s. A modified Hall-Petch-type experimental expression relating hardness to the interphase spacing is proposed.