Recycling of high grade die casting AM series magnesium scrap with the melt conditioned high pressure die casting (MC-HPDC) process

Strict government regulations and environmental concerns are the driving forces behind the increased use of magnesium alloys aimed at weight reductions. This however inevitably leads to increased magnesium alloy scrap and calls for effective recycling processes. In this paper, the melt conditioned high pressure die casting (MC-HPDC) process has been investigated as a physical approach for the recycling of AM series magnesium alloy die casting scrap. Process optimization was required to eliminate hot cracking phenomena. The experimental results showed that intensive melt shearing alters the size and morphology of MgO present in the scrap melt, leading to an effective grain refinement that was reflected in the mechanical properties of the recycled alloy. The MC-HPDC process showed excellent potential as a physical recycling approach for Mg alloy scrap, producing casting with properties comparable to those of fresh Mg alloys.     

Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment

Abstract

In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes.     

Recycling of magnesium alloy AZ91 scrap by a B2O3-containing flux

A new flux was developed specially for recycling of scrap magnesium alloy AZ91 with high iron content. JDMJ in the flux could effectively remove inclusions from the recycled magnesium alloy and its proper addition was about 2.0 wt%. Excessive addition of the flux would result in flux inclusion in the recycled magnesium alloy. B₂O₃ in the flux made the iron concentration in the scrap magnesium alloy decrease from 0.044 wt% to about 0.002 wt% during recycling and its optimal addition was 0.3 wt% by Gaussian Fitting. The tensile properties of the recycled magnesium alloy were greatly improved by about 35%. Weight loss measurement, potentiodynamic study and pitting morphology examination revealed that the corrosion resistance of the recycled magnesium alloy was also greatly improved. The mechanisms of inclusion removing and iron reducing in the scrap magnesium alloy during recycling were discussed thermodynamically and formation of FeB was confirmed as the main reason for iron reducing in the recycled magnesium alloy AZ91 by XRD analysis.     

Segregation Behavior and Evolution Mechanism of Iron-Rich Phases in Molten Magnesium Alloys

A new method has been proposed to prepare Mg-Al-Si master alloys by utilizing scrap Al-Si-Fe alloys with higher Fe levels,which aims to segregate Fe from Al-Si-Fe alloys by Mg melt.The segregation behaviors,microstructure morphology and evolution mechanism of iron-rich phases in Mg-Al-Si alloy melts were studied,after Al-14Si-4Fe(wt%) alloys were added and dissolved completely.In the Mg-Al-Si alloys,iron has very little solubility and tends to combine with other elements to form intermetallic phases,which grow into a deposition layer due to the higher density.During the cooling and solidifying process of Mg-Al-Si melts,the needle-like Al5 SiFe phase in Al-14Si-4Fe alloy evolved into blocky Al_5Fe_2 and Al_(0.7)Fe_3Si_(0.3) phases.Besides,the Fe levels of the Mg-Al-Si master alloys were reduced to 0.017 wt%from nominal content of 0.164 wt%.Based on the above results,this work carried out a semi-quantitative phasecompositions analysis for the deposition layer by relative intensity ratio(RIR) method,and evolution mechanism of the iron-rich phases had also been discussed.This study has paved a new way to regenerate the scrap Al-Si-Fe alloys,which has a great significance of promoting the recycling of aluminum resources.     

重庆镁合金研究与产业的发展现状与建议

重庆市的镁合金产业在短短的3年时间内,在国家和重庆市有关科技计划项目的支持下,经历了从无到有、由小到大的发展过程.在镁合金强化、塑性变形和表面处理等研究方向取得了多项理论成果与专利技术,镁合金产业也已初具规模,形成了从镁金属冶炼、镁合金加工、镁产品应用到废镁回收的完整产业链,镁合金材料已实际应用在摩托车、微型车、自行车、手动工具等产品上.重庆已发展成为我国镁合金研发与产业化的重要基地之一.     

PRODUCTION OF Cu-Cr ALLOYS BY IN SITU REDUCTION OF CHROMIUM OXIDE DURING ELECTRO SLAG CRUCIBLE MELTING (ESCM)

An electro slag crucible melting process for production of copper-chromium alloys is described. The process uses fine copper scrap as a raw material. After the copper scrap is melted, chromium is alloyed with copper by direct reduction of chromium oxide added to the slag. Carbon and aluminum can be used as reductants and the reduction is carried out in situ in the molten slag. Copper chromium ingots containing up to ∼1 wt % chromium were produced by this process. The process serves the dual purpose of recycling copper scrap and alloying remelted copper by chromium. This is the first time that direct reduction has been employed during an electro slag melting process. The in situ reduction technique described has the potential of being a production route for a variety of alloys. It is particularly suitable for production of difficult-to-melt alloys such as copper-chromium.     

有色金属固态回收技术的研究进展

有色金属固态回收避免了重熔,且回收率高、成本低及回收件力学性能优良,具有人的应用前景.介绍了有色金属固态回收技术的原理、特点,重点结合铝合金、镁合金的固态回收研究现状,详细介绍了常规挤压、轧制、循环塑性加工等固态回收技术的研究进展.最后对有色金属固态回收技术的研究和发展提出了一些建议.     

Moderne Entwicklungen von Legierungen für den Leichtbau

Modern development of alloys for light weight components Magnesium alloys fulfil the requirements of low density, good formability and machinability and high recycling potential. Nevertheless applications are still well behind those of competing aluminium materials, particularly in the field of composites. The reasons for this are the higher cost of the primary material (exacerbated by the non-existence of a secondary supply), the limited choice of tailor made alloys and composites and partly the insufficient or lost know how in machining and working. There are also knowledge gaps in the user-industries, which prevent a substitution of conventional materials by magnesium alloys. In order to ensure a greater market for magnesium materials in the future by increasing the quality of existing alloys and processes as well as developing new alloys and processes it is necessary to conduct both long term research and development. This paper describes the existing technologies for the production of aluminium and magnesium components and shows some ongoing development of new production techniques.     

An overview of recycling and treatment of scrap computers

In order to recover valuable materials and to minimize the adverse effects of hazardous materials contained in scrap computers, a dismantling practice is commonly adopted to treat scrap computers. By using the dismantling process, both useful and hazardous materials can be manually separated and retrieved. On the basis of the properties of the retrieved materials, they can be sent to appropriate facilities for further recycling or treatment. Among the retrieved materials, the treatment of hazardous materials from cathode ray tubes (CRT) and printed circuit boards with integrated circuits have drawn considerable attention, thus implying that the proper treatment of such materials can greatly assure the successful recycling of scrap computers. For this reason, this study reviews the available technologies which can be applied to treat and recycle cathode ray tube components and printed circuit boards with integrated circuits. Actual recycling data from a scrap computer recycling plant located in Taiwan are also introduced. The data show that this recycling plant can recover 94.75 wt. % and 45.99 wt. % of useful materials from the main machines (i.e., CPU, power supplier, fan, IC boards, DVD drive, CD drive, hard disk, soft disk, shell casing, etc.) and monitors of scrap computers, respectively.     

Management of scrap computer recycling in Taiwan

It is estimated that approximately 300,000 scrap personal computers are generated each year in Taiwan [S.-L. Chang, A Study on the Scrap Computer Treatment Cost, Environment Protection Administration of Taiwan, December 1998 (in Chinese)]. The disposal of such a huge number of scrap computers presents a difficult task for the island due to the scarcity of landfills and incineration facilities available locally. Also, the hazardous materials contained (i.e., phosphor coatings of cathode ray tubes (CRTs), batteries, polychlorinated biphenyl capacitors, mercury-containing parts, liquid crystal display, high-lead content CRT funnel glass, and plastic containing flame-retardant bromine, etc.) in the scrap computers may seriously pollute the environment if they are not properly disposed of. Therefore, the EPA of Taiwan declared scrap personal computers the producer's recycling responsibility as of July 1997. Under this decree, the manufacturers, importers and sellers of personal computers have to properly recover and recycle the scrapped computers which they originally sell. On June 1, 1998, a producer responsibility recycling program for scrap computers was officially implemented in Taiwan. Under this program, consumers can bring their unwanted personal computers to the designated collection points and receive reward money. Currently, only six computer items are mandated to be recycled in this recycling program. They are notebooks, monitors, hard disks, power supplies, printed circuit boards and main frame shells. This article outlines the current scrap computer recycling system in Taiwan.     

车顶天窗框架废料利用研究及应用

目的 研究汽车车顶天窗框架冲压零件中间废料的利用方法,以减少浪费,降低车身成本。方法 在产品设计、工艺规划及模具开发阶段,借助冲压成形虚拟分析软件,分析零件的成形性和可利用废料的大小,选取合适的零件,合理利用窗框废料并设计开发模具。结果 利用废料同步成形及废料回收再利用这两种天窗框架废料再利用方式均能实现应用,并取得了良好的经济效益。结论 通过冲压同步工程,可以在产品开发和工艺规划时,选择合适的产品,利用好天窗框架废料,实现精益设计和精益制造,满足降低成本的要求。     

稀土镁合金的研究

本文总结了稀土镁合金的研究工作。概要论述了稀土镁合金的发展进程;在稀土元素对镁合金性能影响方面,阐明了稀土元素对镁合金密度、电阻系数和导热系数、热膨胀系数、阻尼容量、晶格常数、弹性模量等物理性能以及对拉伸和蠕变等力学性能的影响。在稀土镁合金微观结构研究方面,总结了稀土相的结构,以及稀土相对合金的强化作用,并提出了我们的一些研究结果。     

多孔镁作为新型骨组织工程材料的研究探索

多孔镁作为骨组织工程材料具有明显的优势.介绍了多孔镁的制备方法,评述了镁基材料作为骨组织工程材料的生物相容性以及在其表面可能制备的生物活性涂层,初步探讨了镁基材料在体内的降解机理,并对多孔镁作为一种新型骨组织工程材料的医用前景进行了展望.     

镁合金阳极氧化的研究与发展现状

综述了镁合金阳极氧化工艺的研究与发展现状，包括着色和密封技术，阳极氧化涂层的反应机理和结构，以及镁和铝阳极氧化之间的异同点，提出了进一步研究和开发的方向。     

A review on magnesium alloys as biodegradable materials

Magnesium alloys attracted great attention as a new kind of degradable biomaterials. One research direction of biomedical magnesium alloys is based on the industrial magnesium alloys system, and another is the self-designed biomedical magnesium alloys from the viewpoint of biomaterials. The mechanical, biocorrosion properties and biocompatibilities of currently reported Mg alloys were summarized in the present paper, with the mechanical properties of bone tissue, the healing period postsurgery, the pathophysiology and toxicology of the alloying elements being discussed. The strategy in the future development of biomedical Mg alloys was proposed.     

A review on magnesium alloys as biodegradable materials

Magnesium alloys attracted great attention as a new kind of degradable biomaterials. One research direction of biomedical magnesium alloys is based on the industrial magnesium alloys system, and another is the self-designed biomedical magnesium alloys from the viewpoint of biomaterials. The mechanical, biocorrosion properties and biocompatibilities of currently reported Mg alloys were summarized in the present paper, with the mechanical properties of bone tissue, the healing period postsurgery, the pathophysiology and toxicology of the alloying elements being discussed. The strategy in the future development of biomedical Mg alloys was proposed.     

长周期结构增强镁合金的研究进展

镁合金具有低密度、高比强度、易回收利用等优点,在电子、汽车、航空航天等领域得到了广泛的应用。但是镁合金强度低、变形加工困难等缺点成为阻碍其大规模应用的主要问题。长周期堆垛有序(LPSO)结构增强镁合金具有较高的强度和较好的塑性,引起了人们的广泛关注。列举了镁合金中5种长周期结构类型及其研究进展,分析了常见的4种长周期结构制备方法的特点,阐述了5种长周期结构特征及其表征方法,分析了长周期结构的强化机制,指出了今后的研究方向。     

Sprühkompaktieren – Entwicklung von Legierungssystemen und Verfahren

Spray Forming – Alloy Development and Process Improvement Today the most common magnesium wrought alloys have acceptable mechanical properties with a limited formability at room temperature. The strength decreases rapidly at temperatures above 150°C. The use of spray forming can provide new wrought alloys, with a resultant improvement in the physical and mechanical properties. Some studies have shown that spray forming techniques are attractive alternatives to improve the mechanical and physical properties of magnesium alloys for the development of new wrought magnesium products.     

铸造镁合金的晶粒细化技术

从晶粒细化方法和晶粒细化机理两个方面总结了不含锆铸造镁合金和含锆铸造镁合金晶粒细化技术的研究进展,并指出新型高效晶粒细化剂的开发和晶粒细化机理的研究是镁合金晶粒细化技术研究的重点.     

The formation of Sr6.33Mg16.67Si13 in magnesium alloy AM50 and its effect on mechanical properties

The increasing use of magnesium castings for automotive components and the number of newly developed alloys raise the question of suitable recycling processes. Remelting offers a high potential of energy saving and thereby improves the live cycle balance of magnesium components. Effective recycling processes are likely to involve the mixing of different alloys but little is known about the interaction of alloying elements. In order to approach this issue, the influence of strontium, silicon and calcium on phase formation and mechanical properties of magnesium alloy AM50 has been investigated. After strontium addition, X-ray diffraction demonstrated the formation of the Al₄Sr and the Mg₁₇Sr₂ phases. However, after simultaneous alloying with strontium, silicon and calcium the ternary Zintl phase Sr_6.33Mg_16.67Si₁₃ was detected. This phase forms preferably instead of Al₄Sr, Mg₁₇Sr₂ and Mg₂Si. Compared to the two strontium-containing phases, precipitates of the ternary Zintl phase exhibit a rather compact morphology. This results in a higher elongation-at-fracture under tensile stress.