| In the 21st century, the balance of resources and the environment and sustainable development has become the most important human issues, energy saving and environmental protection has become a prominent feature of modern industry. The density of magnesium alloy 1.8g/cm3, aluminum alloy,2/3, steel 1/4, is the practical application of the lightest metal. Magnesium alloys have low density, specific strength and specific stiffness, thermal conductivity, and the machinability, good electromagnetic shielding and vibration damping capability and performance, easy recovery and a series of unique advantages, to meet the modern automotive industry weight loss, energy-saving requirements. Magnesium alloy materials has become an important vehicle development, known as the "21st Century Green Engineering Materials."Magnesium alloy parts used in the automotive industry have the following main advantages:light weight, its density is only aluminum 2/3, for use of magnesium alloy vehicle weight can be REduced and, indirectly, reduce fuel consumption and reduce emissions; magnesium alloy higher than the strength of aluminum and steel, than the same stiffness, can replace aluminum and steel parts to withstand a certain load; magnesium alloys have good casting properties and dimensional stability, easy processing, low rejection rate, which can reduce production costs; magnesium alloy has good damping, damping greater than aluminum and cast iron, for the manufacturer of the shell can reduce the noise, for the manufacture of seats, wheels can reduce the vibration, thereby improving vehicle safety and comfort. Therefore, high performance magnesium alloys, magnesium alloys are particularly high temperature magnesium alloys in the automotive industry to further expand the application of the key, but also magnesium alloy automotive research focus.With globalization, the Chinese auto industry is facing unprecedented and severe international competition. reduce vehicle carbon emissions, to achieve light weight and low fuel consumption, lower costs, improve product competitiveness of Chinese auto industry is urgently needed to solve the problem. Magnesium alloy parts used in the automotive industry can further reduce weight, reduce vehicle fuel consumption and emissions, in order to achieve lower vehicle emissions. In addition the application of magnesium alloys can also improve vehicle safety and driving comfort requirements, and improve the car's technical content and quality. Since the 20th century,80 years, magnesium alloy auto parts industry in Europe and North America countries seen a continued trend of rapid growth. SAIC Volkswagen Santana cars started the first domestic case of magnesium alloy gearbox, and achieve mass production. FAW Group, FAW-Volkswagen joint venture company produced by the company Jetta, Audi cars have a considerable number of parts is magnesium alloy parts, but because at that time do not have the FAW Group Corporation production capacity of magnesium alloy die castings, vehicle model in the introduction will be changed to the aluminum magnesium alloy components parts. Currently produced in Volkswagen Jetta A4, Audi A4,, A6 sedan gearbox shell, clutch housing, differential housing, and other parts are magnesium alloy die castings. FAW Car Co. produced cars are red flags and Pentium are facing to achieve through the use of magnesium alloy parts to lose weight, reduce energy consumption and other issues.FAW Foundry Co., Ltd. According to the development trend of magnesium alloy parts in the Ministry of Science and Technology Corporation and the support of research programs, the establishment of a magnesium alloy die-casting production base, its annual production capacity of 1,500 tons of magnesium alloy die castings. Now realized the small quantities of magnesium alloy parts supplier, confirming the magnesium alloy parts in automotive applications is feasible. But now there are still some to be difficult to resolve the technical aspects of casting magnesium alloy components restricts the further application in the automotive industry, mainly in the following three aspects-The strength of magnesium alloy parts is not high enough, can not be used for important structural components, the need to improve the mechanical properties;-Magnesium alloy parts produced in high temperature creep under conditions of use can not meet the sealing requirerments of the shell type parts;-Current commercial corrosion resistance of magnesium alloy lower, unable to meet the coastal climate conditions of use.If the above does not solve the problem is not, magnesium alloys in the automotive industry can not be widely applied, it started for less than the development of high performance magnesium alloy materials, can further enhance the application of magnesium alloy, magnesium alloy and the master The basic law of high temperature creep, the development of high performance automotive products to provide key technical support and basic materials data. The reesearch work for the new proprietary magnesium alloy to improve the FAW Group Corporation grade magnesium alloy die-casting products, technical content and the competitiveness of products are of great significance.In this paper, the development of new high-performance magnesium alloy as the background, according to the actual needs of the automotive industry, systematic study of the addition of alloying elements on Mg-9Al-1Zn system organization and performance of research, in particular its resistance to high temperature creep properties and corrosion resistance, and analysis of the impact of its creep resistance factor, in this based on the development of a new type of high strength, high temperatuRE creep resistant magnesium alloys. The following main elements:(1) Select a good benchmark process performance alloys, and on this basis to develop with independent intellectual property rights, with good casting properties, alloys and relatively low cost alloy, high-performance die-casting magnesium alloy, and to achieve industrial ingot production;(2) systematically study the casting conditions, the rare earth elements (Ce, Y, Nd, etc.) and alloying elements (Mn, Si, Ca, etc.) to add strength to the die-casting magnesium alloy and high temperature creep properties and mechanism of;(3) for heavy-duty diesel engine cylinder head covers room heat requirements and covers the chain torsional requirements, developed with the commercial value of the die-casting magnesium alloy, to achieve commercial production of ingots;(4) to achieve high-pressure casting of magnesium alloys and process optimization of numerical simulation, to achieve mass production.In this study, the above findings, the following conclusions:(1) A new type of magnesium alloy with high-strength and high temperature creep resistance, which is of independent knowledge property, was successfully developed via comprehensive experiments. The experimental results showed that, the tensile strength at room temperatuRE of this new type of alloy was 30MPa higher than that of ZA91D alloy and with the optimal composition, its creep strain was only 1/20 of that of AZ91D alloy. So both the strength and the high-temperature-creep-REsistance of this new type of magnesium alloy are significantly better than those of AZ91D alloys.(2) The Mg-Al-RE-Zn (AWZ) alloy, Mg-Al-Zn-Si-Ca (AZSC) alloy and Mg-Al-Zn-Y (Nd) (AZW) alloy were systematically investigated. Thereinto, AWZ and ANZ alloys, which are developed on the basis of Mg-Al-Zn-Y (Nd) system, exhibited the highest creep REsistance properties. At a temperature of 150℃and a stress of 50MPa, their creep strains were only 1/20 of that of AZ9HP alloys; furthermore, AZSC alloy developed from Mg-Al-Zn-Si-Ca system can also offer good creep REsistance, of which the creep strain is 1/10 of that of AZ91HP alloy under the same conditions.(3) The strengthening mechanism of Mg-Al-Zn-Y (Nd) alloy is solid solution strengthening, and after the creep test at 150℃for 100h, no precipitation phase was observed. The strengthening effect of Mg-Al-Zn-Si-Ca system is attributed to the formation of Mgx(Si,Ca)y at grain boundaries. For Mg-Al-RE-Zn system, the addition of RE leads to the formation of Al11RE3 phase at grain boundaries, resulting in the strengthening of the alloy.(4) Creep test of Mg-Al-RE-Zn alloy system was performed at a temperature of 150℃and a stress of 50MPa for 100h. The results showed that the A111RE3 phase decomposed during the test, and this may account for the poor creep resistance of AE alloy system at 150℃. The cost estimation of three new types of alloys revealed that, at 150℃, the Mg-Al-Zn-Si-Ca system exhibited medium creep resistance, and can be used in the conditions with no special requirements about the creep resistance. Moreover, its cost was lower than that of AZ91D alloy. Though the creep resistance of Mg-Al-Zn-Y(Nd) system is the best and can fully satisfy the conditions which demand high creep resistance performance, its cost is only 8% higher than that of AZ91 alloy.Optimization of processes was conducted by computer numerical simulations. According to the results, batch production of die-casting AZ91Xalloys was carried out. Trail productions of three types of products, including cylinder cap of TA1 engine et al., were also performed. The results of trail production showed that these new types of alloys exhibited excellent processing properties, and completely could be used in the manufacture of auto parts and components. Until now, nearly 1.2 million of auto parts and components arefabricated by using this alloy every year. |
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