Influence of Cu Addition on the Structure,Mechanical and Corrosion Properties of Cast Mg-2%Zn Alloy

Effects of different concentrations of Cu on the structure, mechanical and corrosion properties of Mg-2%Zn alloy were studied by the use of x-ray diffraction, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, standard tensile testing, polarization and electrochemical impedance spectroscopy (EIS) measurements. The average grain size of the alloy decreased from above 1000 μm to about 200 μm with 5 wt.% Cu addition in as-cast condition. Microstructural studies revealed that Mg-2Zn-xCu alloys matrix typically consists of primary α-Mg and MgZnCu and Mg(Zn,Cu)₂ intermetallics which are mainly found at the grain boundaries. The results obtained from mechanical testing ascertained that Cu addition increased the hardness values significantly. Although the addition of 0.5 wt.% Cu improved the ultimate tensile strength and elongation values, more Cu addition (i.e., 5 wt.%) weakened the tensile properties of the alloy by introducing semi-continuous network of brittle intermetallic phases. Based on polarization test results, it can be concluded that Cu eliminates a protective film on Mg-2%Zn alloy surface. Among Mg-2%Zn-x%Cu alloys, the one containing 0.1 wt.% Cu exhibited the best anti-corrosion property. However, further Cu addition increased the volume fraction of intermetallics culminating in corrosion rate enhancement due to the galvanic couple effect. EIS and microstructural analysis also confirmed the polarization results.     

Mechanical Properties and Corrosion Behavior of As-Cast Mg-Zn-Zr-(La) Magnesium Alloys

The effects of La content on the mechanical properties and corrosion behavior of as-cast Mg-Zn-Zr (ZK) magnesium alloys were investigated. The results showed that La addition to ZK60 alloy resulted in a considerable grain refinement and an increase in the volume fraction of second phases by formation of Mg-Zn-La ternary phase. The tensile tests were performed at both room and elevated temperatures. At room temperature, the yield and tensile strengths and elongation-to-fracture significantly increased with 0.2 wt.% La addition, then deteriorated slightly with increasing La additions above 0.2 wt.%. At 200 °C, the yield and tensile strengths continually improved and elongation-to-fracture decreased with increasing La content due to the presence of thermally stable Mg-Zn-La phase. Immersion and electrochemical corrosion tests revealed that the formation of Mg-Zn-La phases led to a higher amount of cathodic sites and preferential corrosion propagation, and thus a decrease in the corrosion resistance of ZK60 alloys.     

Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.     

Al-Ti-B-RE细化剂对Al-7．0Si-0．55Mg合金显微组织和力学性能的影响

研究添加Al-5Ti-lB-RE细化剂对Al-7．0Si-0．55Mg（A357）合金的显微组织和力学性能的影响。先利用真空熔炼技术制各Al-7．0Si-0．55Mg合金,然后在Al-7．0Si-0．55Mg合金中加入不同成分的Al-5Ti-1B-RE中间合金。通过X射线衍射仪（XRD）、金相显微镜（OM）和扫描电子显微镜（SEM）对显微组织和拉伸试样的断口形貌进行观察。在室温下对合金的力学性能进行测试。观察Al-5Ti-1B-RE细化剂的形态以及内部结构,可以发现以TiB,为异质形核核心的TiAl3／Ti2Al20RE的壳层结构相。在Al-7．0Si-0．55Mg合金中加入Al-5Ti-1B-3．0RE细化剂后,抗拉强度会有明显提升,直到0．2％添加量时,抗拉强度会达到峰值。     

Effects of Mn Additions on the Structure,Mechanical Properties,and Corrosion Behavior of Cu-Al-Ni Shape Memory Alloys

The influences of different amount (0.4, 0.7, and 1 wt.%) of Mn addition on the structure, mechanical properties, and corrosion behavior of Cu-Al-Ni shape memory alloys have been studied using differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile test, shape memory effect test, hardness test, and electrochemical test. It was observed that the transformation temperatures, microstructural characteristics, and mechanical properties are highly sensitive to the composition variations. The obtained results show that the transformation temperatures and mechanical properties of Cu-Al-Ni SMAs exhibited the best results with 0.7 wt.% of Mn addition. These kinds of enhancements are mainly due to the type, amount, and morphology of the martensite phase, including the grain refinement. The result of electrochemical test showed that an increment in Mn content up to 0.7 wt.% improved the corrosion resistance of Cu-Al-Ni SMA. However, further increase of Mn content decreases the corrosion resistance of the alloy.     

Grain refinement effect of La2(CO3)3 on AZ91 magnesium alloy

The La2(CO3)3 addition makes the grain of AZ91 alloy be refined obviously.The average primary dendrite size of the alloy decreases from 150 to 50 μm.The microstructure of typical dendrite turns into the equal-axed grain with the addition of 2.5 wt.% La2(CO3)3 refiner.The mechanical properties tests indicate that the tensile strength and especially elongation of the alloys are improved with the addition of La2(CO3)3 and their maximum enhancing rates based on the La2(CO3)3-free AZ91 alloy are 26% and 5.2 times at 2.5 wt.% La2(CO3)3 refiner respectively.     

Effects of Minor Zr and Sr on As-Cast Microstructure and Mechanical Properties of Mg-4Y-1.2Mn-1Zn (wt.%) Magnesium Alloy

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg-4Y-1.2Mn-1Zn (wt.%) alloy were investigated using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The microstructural results indicate that small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not cause an obvious change in the morphology and distribution of the Mg₁₂YZn phase in the alloy. The tensile and creep tests indicate that, although small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not have obvious effects on the creep properties of the alloy, the tensile properties at room temperature and 300 °C for the alloys added with Zr and/or Sr are improved. Among the Zr- and/or Sr-containing alloys, the alloy specifically added with of 0.5 wt.% Zr + 0.1 wt.% Sr obtains the optimum tensile properties, and is followed by the alloys added with 0.5 wt.% Zr and 0.1 wt.% Sr.     

Microstructure and mechanical performance of a secondary cast aluminium piston alloy with minor element additions

The effect of individual and combined minor element additions (Sr, Sb, Mn, Cr and Al-5Ti-1B grain refiner) on microstructure and mechanical performance of a secondary cast aluminium piston alloy, with 1 wt-% Fe was investigated. It was observed that addition of Cr of up to 1% was better than a 0.53%Mn addition in improving tensile strength, impact energy and percent elongation of the alloy. The high mechanical performance recorded with addition of 1%Cr alloy was attributed to the significant reduction in porosity levels compared to all other minor element additions. It also resulted in a microstructure with fine compact intermetallic compounds. Other element additions also resulted in improved mechanical properties with 0.53%Mn performing better than 0.3%Mn + 0.2%Cr. Marginal improvements in mechanical performance were recorded with addition of 0.02%Sr (or 0.05%) and 0.02%Sb individually or in combination with 0.53%Mn. This was attributed to general increase in porosity and volume fraction of intermetallics.     

稀土镧对Al-0.6Mg-0.7Si-0.2Mn汽车板材机械及腐蚀性能的影响

采用SEM、OM、拉伸试验（常温/高温）、弯曲试验和晶间腐蚀试验等测试方法,对添加不同含量稀土元素镧的Al-Mg-Si-Mn合金组织、机械性能及耐腐蚀性能等进行研究,分析稀土元素镧对合金机械和腐蚀性能的影响。结果表明,随La元素的添加,合金的铸态组织逐渐细化,第二相形貌得到了改善,同时减薄了该合金型材粗晶区厚度,提高了Al-Mg-Si-Mn合金的机械性能和耐腐蚀性能。当La添加量为0.2 wt.%时,晶粒细化效果最好,型材粗晶区最薄;La含量大于0.2 wt.%时,过量的La形成的初生相与合金晶粒细化剂中的Ti相互作用,减少了异质形核核心的数量,导致晶粒粗化现象,恶化合金的机械性能和耐腐蚀性能。     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

Effect of Homogenization Temperature on Microstructure and Conductivity of Al-Mg-Si-Ce Alloy

Microstructure evolution of Al-0.2wt.%Mg-0.36wt.%Si-0.3wt.%Ce alloy at three different homogenization temperatures for 6 h was observed by optical microscopy, scanning electron microscopy, and x-ray diffraction. Conductivity and tensile properties of the alloy were tested. Results indicate that homogenization temperature has little effect on the macro-segregation and grain size of the as-cast Al-Mg-Si-Ce alloy; however, it has a significant effect on the conductivity. The conductivity is first improved to a maximum value of about 57.3% IACS with homogenization temperature increasing to 560 °C (2.7% higher than that of the as-cast sample), and then decreased when the temperature continuously increasing. The main contributor is considered to be vacancy concentration, which is directly related to the lattice distortion, thus affects the conductivity. The studied homogenization temperatures almost make no difference among the tensile properties of the alloy. The best homogenization temperature for Al-0.2wt.%Mg-0.36wt.%Si-0.3wt.%Ce alloy is 560 °C with the highest conductivity and no decrement of strength.     

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.     

Enhanced mechanical properties and formability of hot-rolled Mg–Zn–Mn alloy by Ca and Sm alloying

In order to broaden the application of wrought Mg alloy sheets in the automotive industry, the influence of Ca and Sm alloying on the texture evolution, mechanical properties, and formability of a hot-rolled Mg–2Zn–0.2Mn alloy was investigated by OM, XRD, SEM, EBSD, tensile tests, and Erichsen test. The results showed that the average grain size and basal texture intensity of Mg–2Zn–0.2Mn alloys were remarkably decreased after Ca and Sm additions. 0.64 wt.% Ca or 0.48 wt.% Sm addition significantly increased the tensile strength, ductility and formability. Moreover, the synergetic addition of Sm and Ca improved the ductility and formability of Mg–2Zn–0.2Mn alloy, which was due to the change of Ca distribution and further reduction of the size of Ca-containing particles by Sm addition. The results provided a possibility of replacing RE elements with Ca and Sm in Mg alloys which bring about outstanding mechanical properties and formability.     

Grain Refiner Effect on the Microstructure and Mechanical Properties of the A356 Automotive Wheels

A356 aluminum alloy automotive wheels, 17 inch in diameter, were produced by low-pressure die casting. Contents of Al-5Ti-B (ATB) master alloy were added from 0 to 0.79 wt.%. Microstructural and mechanical properties were evaluated under industrial casting process conditions. The obtained results from mechanical testing provide evidence that additions of 0.13 and 0.27 wt.% of ATB have an improvement on the mechanical performance of the automotive wheels. This can be compared with the use of a grain refiner’s higher concentrations, leading to a significant reduction in the cost-benefit ratio for the manufacturing of A356 automotive wheels.     

Effect of Grain Refinement and Cooling Rate on the Microstructure and Mechanical Properties of Secondary Al-Si-Cu Alloys

The effect of AlTi5B1 grain refinement and different solidification rates on metallurgical and mechanical properties of a secondary AlSi7Cu3Mg alloy is reported. While the Ti content ranges from 0.04 up to 0.225 wt.%, the cooling rate varies between 0.1 and 5.5 °C/s. Metallographic and thermal analysis techniques have been used to quantitatively examine the macro- and microstructural changes occurring with grain refiner addition at various cooling rates. The results indicate that a small AlTi5B1 addition produces the greatest refinement, while no significant reduction of grain size is obtained with a great amount of grain refiner. On increasing the cooling rate, a lower amount of AlTi5B1 master alloy is necessary to produce a uniform grain size throughout the casting. The combined addition of AlTi5B1 and Sr does not produce any reciprocal interaction or effect on primary α-Al and eutectic solidification. The grain refinement improves the plastic behavior of the alloy and increases the reliability of castings, as evidenced by the Weibull statistics.     

Microstructure,anticorrosion, biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications, Mg?6Zn?0.3Mn?xCa (x=0, 0.2 and 0.5, wt.%) alloys were prepared by semi-continuous casting followed by hot-extrusion technique. The microstructure and mechanical properties of Mg?6Zn?0.3Mn?xCa alloys were investigated using the optical microscope, scanning electron microscope and tensile testing. Results indicated that minor Ca addition can slightly refine grains of the extruded Mg?6Zn?0.3Mn alloy and improve its strength. When 0.2 wt.% and 0.5 wt.% Ca were added, the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2 μm, respectively. Of the three alloys studied, the alloy with 0.5 wt.% Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%. The corrosion behaviour, cell viability and antibacterial activities of alloys studied were also evaluated. Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca₂Mg₆Zn₃ phases. Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg?6Zn?0.3Mn?0.5Ca alloy compared to Mg?6Zn?0.3Mn and Mg?6Zn?0.3Mn? 0.2Ca alloys. The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.     

Effect of Y on microstructure evolution and mechanical properties of Mg−4Li−3Al alloys

To obtain magnesium alloys with a low density and improved mechanical properties, Y element was added into Mg−4Li−3Al (wt.%) alloys, and the effect of Y content on microstructure evolution and mechanical properties was investigated by using optical microscopy, scanning electron microscopy and tensile tests. The results show that mechanical properties of as-cast Mg−4Li−3Al alloys with Y addition are significantly improved as a result of hot extrusion. The best comprehensive mechanical properties are obtained in hot-extruded Mg−4Li−3Al−1.5Y alloy, which possesses high ultimate tensile strength (UTS=248 MPa) and elongation (δ=27%). The improvement of mechanical properties of hot-extruded Mg−4Li−3Al−1.5Y alloy was mainly attributed to combined effects of grain refinement, solid solution strengthening and precipitation strengthening.     

Effect of rare earth on the microstructure and mechanical properties of as-cast Cu-30Ni alloy

Cu-30Ni-xRE (x = 0–0.213) alloys were prepared by a metal mould casting method. The effect of RE on the microstructure and mechanical properties of the alloys was investigated using optical microscope, scanning electronic microscope with energy-dispersive spectrometer, X-ray diffraction, and mechanical test. The results show that RE has obvious effect on refining dendrite structure and grain size, as well as on purifying the melting of Cu-30Ni alloy. With the increase of RE content, the ultimate tensile strength, yield strength, and elongation increase at first and then decrease after adding RE more than 0.095 wt.%. Cu-30Ni-0.095RE alloy possesses preferable mechanical properties, i.e., the ultimate tensile strength, yield strength, and elongation are 308 MPa, 125 MPa, and 51.2%, respectively. The microstructure and mechanical properties are worsened with increasing RE content more than 0.095 wt.%. The improvement of mechanical properties of Cu-30Ni-0.095RE alloy is attributed to RE refining microstructure and purifying the matrix.     

Influence of Annealing Heat Treatment and Cr, Mg, and Ti Alloying on the Mechanical Properties of High-Silicon Cast Iron

The influence of annealing on the mechanical properties of high-silicon cast iron for three alloys with distinct chromium levels was investigated. Each alloy was melted either with or without the addition of Ti and Mg. These changes in the chemical composition and heat treatment aimed to improve the material’s mechanical properties by inhibiting the formation of large columnar crystals, netlike laminae, precipitation of coarse packs of graphite, changing the length and morphology of graphite, and rounding the extremities of the flakes to minimize the stress concentration. For alloys with 0.07 wt.% Cr, the annealing reduced the impact resistance and tensile strength due to an enhanced precipitation of refined carbides and the formation of interdendritic complex nets. Annealing the alloys containing Ti and Mg led to a decrease in the mechanical strength and an increase in the toughness. Alloys containing approximately 2 wt.% Cr achieved better mechanical properties as compared to the original alloy. However, with the addition of Ti and Mg to alloys containing 2% Cr, the chromium carbide formation was inhibited, impairing the mechanical properties. In the third alloy, with 3.5 wt.% of Cr additions, the mechanical strength improved. The annealing promoted a decrease in both hardness and amount of iron and silicon complex carbides. However, it led to a chromium carbide formation, which influenced the mechanical characteristics of the matrix of the studied material.     

Effect of Zr additions on mechanical properties of an ASTM F-75 alloy

The ASTM F-75 alloy is widely used for orthopedic implants. In order to improve the mechanical properties, in particular ductility, the components fabricated by the investment casting process are generally heat treated to partially dissolve carbide precipitates. In the present work, the effect of Zr additions on the mechanical properties of a solution-treated ASTM F-75 alloy was studied. The Zr contents were 0.1, 0.05, 0.017, and 0%. Among the alloys chemically modified, that with 0.017% of Zr provided an appropriate microstructure for thermal processing. After the solution treatment, the latter alloy showed markedly increased tensile properties when compared with the Zr-free alloy. This was associated to the role of Zr as a grain refiner, as revealed by the microstructural analysis. Thus, the addition of Zr constitutes an effective way to enhance the mechanical properties of solution-treated alloys.