The Effects of Rare Earth Elements on High Pressure Die Casting Mg Alloys

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2019. 2. 신광선.마그네슘합금은 높은 열전도도, 비강도 및 기계 가공성 등 우수한 특성을 가지고 있으며 일반적으로 고압 다이캐스팅(HPDC) 공정을 통해 제조되고 있다. 현재 스티어링휠, 엔진블록, 오일팬 등의 자동차 부품들은 다른 부품에 비해 기술적 어려움과 원가의 문제점을 가지고 있음에도 불구하고, 전체 자동차 무게에 있어 큰 비중을 차지하여 경량화 효과를 크게 얻을 수 있다. 본 연구에서는350 ton 진공 다이캐스팅 장비를 이용하여 Mg-Al 합금에 Sn, Ca, Sr, Y 및 Mm 의 원소들을 첨가하여 다양한 합금계를 제조하였으며 첨가 원소에 따른 다이캐스팅 시편의 미세조직 변화와 기계적 특성을 평가하였다. 또한 120oC에서 0.5, 1,2,4,8,12시간동안 열처리하고 기계특성 및 미세조직에 대해 고찰 했다. 본 연구에서 SEM 및 XRD등 분석 기계를 통해서 모두 시편들의 미세조직 하고 석출물을 분석하였다.Magnesium is the 12th element in the element pool, the 8th abundant element in the earth. It attracted many researchers applied on structural materials because of its low density. As the lightest structural materials, magnesium alloys are very suitable for the applications of automotive industry where vehicle weight reduction and consequently energy saving are becoming the word focus. It is well known that the possible application of AZ91 and AM60 alloys is still restricted due to some problems. For example, the two alloys are unsuitable for manufacturing parts operating at temperatures higher than 120 °C. In addition, the strength and ductility of the commercial AZ91 and AM60 alloys do not simultaneously satisfy the requirement of some important parts. For example, AZ91 alloys strength is relatively highhowever, the ductility of the alloy is not so good due to the high Al content. Although AM60 alloy has a high ductility, its strength is relatively poor. Various alloying and/or micro-alloying elements, such as Ce, Nd, Y, Si, Ca, Ti, B, Sr, Sb, Bi, Pr and so on, have been chosen to further improve the mechanical properties of AZ91 alloy. With the addition of yttrium, the AZ91D alloy is found to have good mechanical properties with the tensile strength of 270 MPa and elongation of 11%. For the modified-AM60 alloys, various alloying and/or micro-alloying elements, such as Ca, Sn, Y, Si, Ti, Ag, Nd, B, RE, Sr, Ce and so on, have been chosen to further enhance the mechanical properties of AM60 alloys. In this article, the effect of rare earth elements on commercial Mg alloys were observed. For developing high strength die casting Mg alloys, various RE elements were used for precipitating new phase to achieve the goal. Tensile test, corrosion test and other mechanical test was carried out, and SEM and EDS was used for the analysis of section part. In the first part, the process of developing new alloys will be introduced and the influence of different elements on Mg alloys will be compared as well. Sr, Y, Sn, Ca and Zn were added into Mg-Al based alloys. The specimen was produce 350t cold chamber die-casting machine. In the second part, the practical die casting process and parameters will be introduced. The strength and elongation was observed. Microstructure was observed by SEM and OM. Then phase and precipitate were observed by EDS and XRD. Compared with simulated results, the phase was observed as expcted. At last, the specimen were heat treated at 120 oC for 0.5h to 12h. After heat treatment, the mechanical properties was improved, and due to different phase in different alloys, some properties was improved significantly.1. Introduction ..............................................................................1 1.1 Mg Alloys ............................................................................................1 1.2 Die Casting ..........................................................................................4 1.3 Fracture in Die Casting ........................................................................8 1.4 Research Objectives ...........................................................................10 2. Experiment Procedure ............................................................10 2.1 Alloy Design ......................................................................................10 2.2 Experiment Condition ........................................................................13 2.2.1 Die Casting Condition ..............................................................13 2.2.2 Tensile Test Condition ..............................................................16 2.2.3 Heat Treatment Condition ........................................................16 2.3 Characterization of microstructure and mechanical properties .........16 2.3.1 Observation of microstructure ..................................................16 3. Results and Discussions .........................................................17 3.1 Thermodynamic prediction of precipitates ........................................17 3.2 Mechanical Properties at Room Temperature (RT) of As-casted Specimen ............................................................................................25 3.3 Microstructure ....................................................................................27 3.4 Mechanical Properties at Room Temperature after heat treatment ...44 4. Conclusions ............................................................................51 Reference ....................................................................................53Maste

Structure-Property Relationships of Magnesium Alloys

First, I would like to acknowledge Meridian Technologies Inc., for their contributions in the materials, equipment and facilities that made this work possible. Second, this project was also partly funded By AUTO21 Network of Centers of Excellence, an automotive research and development program focusing on issues relating to the automobile in the 21st century. AUTO21, member of the Networks of Centers of Excellence of Canada program is funded by the Natrual Science and Engineering Research Council (NSERCT), the Social Science and Humanities Research Council (SSHRC) and multiple industries. Third, I would like to thank the invaluable inputs and guidance provided by Dr.Jon weiler, during the course of this research. Fourth, I would like to thank Dr. Klassen’s group research for their assistance during microindentation testing procedure. Finally, I would like to thank my advisor, Dr, Jeff Wood for his patience, guidance, and generosity over the past two years. His constant support and encouragement were indispensable factors behind the successful completion of this research

Applications of High-Pressure Die-Casting (HPDC) Magnesium Alloys in Industry

High-pressure die-cast (HPDC) magnesium alloys have seen diverse applications in the automotive industry, primarily driven by requirements in internal combustion engine (ICE) vehicles. As the automotive industry is transitioning to an electric vehicle (EV) architecture, there is a great potential for novel applications to improve driving range efficiency. In addition, there is a trend toward larger-sized automotive die castings and an increased interest in aerospace applications due to weight reduction. In this chapter, we reviewed the traditional automotive structural applications in ICE vehicles, as well as current and potential future EV and aerospace applications of HPDC magnesium alloys. The structural applications using AM50, AM60, AZ91 and AE44 magnesium alloys in traditional vehicles can be applied to modern EVs. Additionally, magnesium alloys with varying degrees of higher thermal conductivity, improved castability, superior high temperature properties and flammability need to be developed to replace battery and aerospace in-cabin-related structural materials to meet all safety requirements. Several newly developed magnesium alloys with superior castability are also reviewed for potential automotive and aerospace applications

Mg/hydroxyapatite composites for potential bio-medical applications

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.Depending on an excellent combination of high mechanical property and fracture toughness, metallic biomaterials have been widely accepted for clinical application of bone fixation. However, some prominent disadvantages such as stress shielding effect due to their high elastic modulus, poisonous ions released by corrosion or mechanical wear [Puleo and Huh, 1995] definitely restrict their effective performance in-service. In addition, patients also have to bear the pain resulted from second surgery for removing implants. Although bio-degradable polymers and ceramics seem to solve the tough problem as promising substitutes, the low mechanical property and rapid corrosion rate make them fail to qualify against the bear-loading requirement in body. Therefore, we desperately look for a non-toxic suitable material for medical application which possesses appropriate mechanical properties, and favourable corrosion resistance

Comportamiento mecánico a alta velocidad de deformación de aleaciones de magnesio

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, leída el 17-12-2012Depto. de Ingeniería Química y de MaterialesFac. de Ciencias QuímicasTRUEunpu

CORROSION BEHAVIOUR OF THE AZ31 MAGNESIUM ALLOY AND SURFACE TREATMENTS FOR ITS CORROSION PROTECTION

Nowadays environmental conservation forces the transportation industry to manufacture lighter and low emissions transport vehicles. In this contest, magnesium alloys have found increasing attention by the automotive industry because of their low density associated with good mechanical properties. However the low corrosion resistance of magnesium alloys in wet environments is still a limiting factor against their widespread diffusion. The aim of this research is both studying the correlation between microstructure and corrosion behaviour of a AZ31 magnesium alloy and developing eco-friendly protective technologies. In particular inhibitors and surface pretreatments with different organic compounds have been investigated. The effect of microstructure on corrosion resistance of AZ31 alloy has been analyzed through a comparative study between the electrochemical behaviour of as-cast and hot rolled AZ31. Environmentally friendly sodium salts of mono-carboxylic acids have been studied as inhibitors of AZ31 alloy corrosion in a standard saline solution. Moreover, long chain sodium mono-carboxylates have been tested as promoters of conversion coatings for this alloy. Finally, significant improvements have been achieved by modifying the protective coatings obtained by 3-mercapto-propyl-trimethoxysilane through cerium nitrate or oxide nanoparticle additions

Alloying Elements of Magnesium Alloys: A Literature Review

Magnesium alloys are the lightest structural metal. The lightness is the main reason for the interest for Mg in various industrial and clinical applications, in which lightweight structures are in high demand. Recent research and developments on magnesium Mg alloys are reviewed. A particular attention is focused on binary and ternary Mg alloys consisting mainly of Al, Zn, Mn, Ca and rare earth (RE) elements. The effects of different alloying elements on the microstructure, the mechanical and the corrosion properties of Mg alloys are described. Alloying induces modifications of the microstructural characteristics leading to strengthening mechanisms, improving then the ductility and the mechanical properties of pure Mg

Mechanical properties and deformation behaviour of high-pressure die-cast magnesium-aluminium based alloys.

Due to the low-density and high-specific strength, magnesium alloys are expected to enjoy increasing use in automotive and aerospace industries. However, relative to aluminium alloys, the applications of die-cast magnesium alloys remain limited, mainly due to their inadequate mechanical properties. The research presented here provided a better understanding of the deformation behaviour of die-cast magnesium alloys. This research demonstrates that the deformation behaviour of die-cast magnesium-aluminium based alloys can be separated into four stages. Decomposition of stress-strain curve into these different stages has provided insights into the improved measurement of proof strength, the role of aluminium solute in moderating strain-rate sensitivity, the interactions of slip and twinning deformation systems to understand total anelasticity and the contributions of different slip and twinning deformation mechanisms to the overall deformation behaviour. This research is a milestone in developing understanding of the deformation mechanisms in die-cast magnesium alloys and will provide the foundation for future development of improved structural alloys