汽车用压铸镁合金的开发与应用新进展

镁合金以其轻质、减振、防辐射等特点在汽车工业中获得了广泛应用。本文较详细地论述了镁合金的特性、工艺特点、用途以及开发应用领域和前景,汽车用压铸镁合金的开发技术、国内外现状、发展水平和趋势。     

压铸镁合金的应用与开发

镁合金质量轻、比强度和比刚度高以及良好的铸造性能、电磁屏蔽和减振性能等特点,使镁合金成为当今工业产品应用增长速度最快的金属材料。随着镁合金应用领域不断扩大,新型镁合金的研究与开发也不断涌现。本文综述了压铸镁合金的性能特点及其在汽车、电子等工业上的应用及其发展趋势,分析了我国镁合金行业的现状与发展前景。     

压铸镁合金在汽车中的应用及其发展前景

论述了镁工业概况及镁合金压铸件在汽车工业中的应用,指出我国镁合金压铸件在汽车中的应用处于初级阶段,发展前景广阔。     

镁合金压铸成型技术问世

沈阳工业大学科技处近日向社会推出镁合金压铸成型技术。据介绍，镁合金具有密度小、比强度大、铸造性能和机加工性能优良、减震性和屏蔽性好等优点，镁合金压铸近年来表现出强劲发展势头。压铸成型过程具有有压力和高速度充型的特点，是生产镁合金零部件的有效方法。镁合金压铸成型技术主要包括镁合金熔化及保护、压铸模设计、工艺过程控制、承力零部件的后热处理等。     

镁合金的研究应用及最新进展

镁合金由于具有质量轻、比强度和比刚度高以及良好的铸造性能等特点,在理论研究和实际应用上引起了人们极大的关注.近年来,世界各国纷纷致力于镁合金的研究开发.本文综述了镁合金的性能特点、镁合金的合金系列、镁合金在汽车、电子等工业上的应用以及镁合金的发展动向,分析了我国镁合金行业的现状和发展前景.     

双螺旋流变压铸AZ91D镁合金的研究

液态压铸是镁合金最主要的成形方式,但液态压铸件存在气孔等缺陷,限制了镁合金的进一步推广使用。介绍了采用双螺旋流变制浆技术,对镁合金AZ91D进行了流变压铸研究。首先,将镁合金AZ91D熔体浇入到双螺旋流变制浆机中,然后根据不同工艺参数制备流变镁合金浆料,待制浆结束后,将半固态浆料转移到压铸机内,制得半固态压铸件。采用Micro-Image Analysis&Process(MIAP)软件分析了双螺旋流变制浆工艺参数(搅拌温度、搅拌时间和转速)对镁合金AZ91D的初生相晶粒大小的影响,并研究了镁合金压铸成形性。结果表明:随着搅拌温度的降低,晶粒尺寸变化不是很大;随着搅拌时间延长,镁合金晶粒尺寸逐渐增大;随着搅拌速度的增加,镁合金平均晶粒尺寸减少。镁合金流变压铸件中的初生α相由搅拌中形成的球状晶及压铸过程中二次凝固形成的更为细小的球状晶组成。对比了普通压铸件与流变压铸件热处理后的力学性能,流变压铸件的力学性能得到大幅提高,其原因归结为铸态组织的细小和均匀化。     

工艺参数对压铸AM60B合金组织缺陷的影响

采用液态压铸技术，研究了压铸工艺参数对AM60B合金组织缺陷的影响。试验结果表明，当浇注温度为680℃、模具温度为180℃、压射速度为3．0m/s、压射比压为75MPa时，压铸镁合金AM60B可以获得组织均匀细小、表面光滑、缺陷极少的铸件。     

镁及镁合金加工技术的现代化进展

本文简要介绍镁及镁合金加工业的发展现状，重点论述新型镁合金研究及镁合金加工技术（熔炼、压铸、挤压、锻压、轧制等）开发方面的现代化进展与发展前景。     

中国铝合金压铸业的发展及现状

前言Foreword压力铸造工艺的诸多特点,使其在提高有色金属合金铸件的精度水平、生产效率、表面质量等方面显示出了巨大优势。随着汽车、摩托车等工业的发展,以及提高压铸件质量、节省能耗、降低污染等设计要求的实现,有色金属合金压铸件、特别是轻合金(铝及镁合金)压铸件的应用范围在快速扩张。有资料表明:工业发达国家用铝合金及镁合金铸件代替钢铁铸件正在成为重要的发展趋势。目前压铸已成为汽车用铝合金成形过程中应用最广泛的工艺之一,在各种汽车成型工艺方法中占49%。     

镁合金研究开发现状与展望

介绍了镁合金研究开发和应用领域的国内外发展动态,耐热镁合金、耐蚀镁合金、高强高韧镁合金、变形镁合金等高性能镁合金材料的最新发展,镁合金压铸、半固态铸造、挤压铸造、超塑性、冲锻等成形技术的最新开发研究成果,指出了镁合金研究开发的发展趋势,提出了我国在镁和镁合金研究开发和应用领域需要注意的问题。     

镁合金应用现状及铸造技术研究进展

介绍了镁合金特点及在电子、汽车、自行车及生物医用材料领域的应用状况;阐述了镁合金的各种铸造成型方法及一些新型工艺的前景;分析了典型的合金元素对镁合金铸件性能的影响。研究表明,开发新型的铸造成型工艺、提升装备水平、通过控制成分提高合金性能是扩大镁合金在各个领域应用的关键。     

Formation of defect bands in high pressure die cast magnesium alloys

Die cast magnesium components are being increasingly used worldwide because of the excellent castability and properties that magnesium alloys offer. High pressure die casting of thin-walled components is particularly suitable because of the excellent flow characteristics of molten magnesium alloys. Typical automotive applications for thin-walled castings include components such as instrument panels, steering wheels, door frames and seat frames. These applications require optimisation of the quality and performance of the castings. It has been found that bands of porosity or segregation which follow contours parallel to the surface of the casting are formed under certain casting conditions in thin-walled magnesium high pressure die castings. The presence of this type of defect can have a significant effect on the mechanical properties. This paper investigates the effect of varied casting conditions on casting integrity and the appearance of the bands. A rationale for understanding the origin of these defects is related to the solidification behaviour, the mushy zone rheological properties and the filling pattern of the casting with associated shearing of the mushy zone. Methods to optimise the process parameters to control the occurrence of the banded defects, and thereby optimise the quality of high pressure die cast magnesium components, are outlined.     

镁合金板带铸轧技术与进展

镁合金板材的应用需求正在扩大,而板带连续铸轧一直被认为是制造镁合金薄板的一种最有效的生产方式。通过综合回顾镁合金板材轧制技术和板材铸轧技术的发展与现状,分析讨论各种连续铸轧和半固态铸轧的工艺技术特点及其优缺点,并介绍了镁合金板带铸轧的新技术发展动向以及金属强制均匀化理论技术在铸轧镁合金薄板中的优越性和适用性。实验结果表明,金属熔体强制均匀化处理和加工成形可有效增加均质熔体的形核率,对合金凝固组织的均匀化、细化效果显著。     

Relationships between process parameters and temperature field of roll casting for wide sheet made of AZ61 magnesium alloy: Finite element method

In recent years, wide sheet made of AZ61 wrought magnesium alloys has been widely studied and applied in industry. Thin roll-casting technology for the new wrought magnesium alloy can provide acceptable quality wide and thin sheet made of AZ61 magnesium alloy. To study the influences of roll-casting process parameters on temperature field for wide and thin sheet made of AZ61 magnesium alloy plates, some simplification and assumptions have been done by characteristics of magnesium alloy. Two-dimensional FEM model for roll-casting has been established along casting direction. Simulations of temperature fields of the plates have been done by using finite element analysis ANSYS software. A series of researches on the temperature distributions under different process parameters (pouring temperature, heat-transfer coefficients and casting speeds) have been done. The simulation results and the literature about the casting process of the relevant theory are the same. The simulation results show that the process parameters of rapid-casting process for AZ61 magnesium alloy are mutual influenced on the temperature fields of wide sheet made of AZ61 magnesium alloy.     

Semi‐Solid Processing of Metal Alloys

Semi‐solid metal casting is an innovative technology for the production of near‐net‐shape parts with demanding mechanical properties. The paper describes different processing routes and materials for semi‐solid‐metal casting (SSM), which have been investigated and also partially developed at the Foundry‐Institute of Aachen University. The standard thixocasting process for aluminium, highly reactive magnesium alloys and steel alloys with high melting points was investigated under variation of a wide range of process parameters. Specially adapted pre‐material production and reheating methods were developed for different materials and their application and future potential is pointed out. The thixocasting experiments were executed on a modified high pressure die‐casting machine with a specially designed “step‐die” providing wall thicknesses from 0.5 to 25 mm. The mechanical properties were tested in dependence of the wall thickness and the metal velocity. The results of these examination show high tensile strength values in combination with very good elongations. The rheocasting process is a new SSM‐forming method with liquid melt as feed‐stock and a high recycling potential. The research results of RCP‐technology (Rheo‐Container‐Process) invented at the Foundry‐Institute and of the Cooling‐Channel‐Process for aluminium and magnesium alloys are promising and are presented in this paper. Studies on semi‐solid processing of magnesium alloys and mixtures of them were conducted by Thixomolding^TM. To establish the most adequate process parameters, the temperature and the mixture relations were varied. Using a mould for tensile test specimens, the mechanical properties and the microstructure evolution could be evaluated. The chemical composition of the different phases was determined using SEM and EDX technologies. Evaluations of the flowing properties were conducted using a spiral mould with a total length of 2m and a cross section of 20mm x 1.5mm.     

Development of the as-cast microstructure in magnesium–aluminium alloys

This paper presents an overview of several projects undertaken at CAST to increase our understanding of the solidification characteristics of Mg–Al alloys. With the increased use of magnesium alloys, and with casting dominating as a production route, there is a need for a more comprehensive understanding of the mechanisms of solidification and defect formation to allow further optimisation of alloys and casting processes. The paper starts with considering the formation of the primary magnesium dendrites and the means for grain refinement of magnesium–aluminium alloys. The Mg–Al system is then shown to display a range of eutectic morphologies for increasing aluminium content, ranging from a divorced structure, through several intermediate structures, to a fully lamellar structure at the eutectic composition. The eutectic also influences discontinuous precipitation which occurs in the aluminium-rich regions of the magnesium phase. The paper concludes with a section on porosity formation as a function of aluminium content and an outline of the mechanism responsible for the formation of banded defects in magnesium alloys, particularly in products made in pressure assisted casting processes.     

Microstructure and Corrosion Characterization of Squeeze Cast AM50 Magnesium Alloys

Squeeze casting of magnesium alloys potentially can be used in lightweight chassis components such as control arms and knuckles. This study documents the microstructural analysis and corrosion behavior of AM50 alloys squeeze cast at different pressures between 40 and 120 MPa and compares them with high-pressure die cast (HPDC) AM50 alloy castings and an AM50 squeeze cast prototype control arm. Although the corrosion rates of the squeeze cast samples are slightly higher than those observed for the HPDC AM50 alloy, the former does produce virtually porosity-free castings that are required for structural applications like control arms and wheels. This outcome is extremely encouraging as it provides an opportunity for additional alloy and process development by squeeze casting that has remained relatively unexplored for magnesium alloys compared with aluminum. Among the microstructural parameters analyzed, it seems that the β-phase interfacial area, indicating a greater degree of β network, leads to a lower corrosion rate. Weight loss was the better method for determining corrosion behavior in these alloys that contain a large fraction of second phase, which can cause perturbations to an overall uniform surface corrosion behavior.