镁合金再生后组织与性能的研究

研究了加入不同质量回收料的再生镁合金中夹杂物、组织及性能.结果表明,再生镁合金中夹杂物数量随着镁合金废料比例的增加而增多,夹杂物成分主要为镁的氧化物和少量铝的氧化物,且夹杂伴随着气孔产生;力学性能和抗腐蚀性能都随着原料中回收废料的比例增加而降低;镁合金的再利用必须经过精炼,将夹杂物含量控制在一定范围之内;镁合金再生具有明显的组织遗传性;利用气体喷吹精炼装置对回收镁合金进行精炼,取得满意效果.     

消失模铸造镁合金废旧料的回用特征

消失模铸造应用于镁台金零件的生产，废旧料随之产生。本文对消失模铸造镁合金废旧料的特点进行了概述，对加入不同比例消失模铸造镁合金废旧料时的镁合金的组织和性能进行了测试研究。结果表明：镁合金中夹杂物数量随废旧料比例的增加而增多，且夹杂伴随着气孔产生；力学性能和抗腐蚀性能都随原料中废旧料比例的增加而降低，全新料与全废旧料比较，性能的降幅在30％左右。为了实现废旧料的回收利用，废旧料的加入数量不宜过多，对金属液实施充分的精练除渣是获得合格铸件的保障；去除夹杂是消失模铸造镁合金废料回用的主要任务。     

镁合金熔体净化工艺的研究

研究了镁合金再生过程中熔体内夹杂物含量、尺寸与静置时间的关系,以及主要合金成分和杂质元素含量的变化规律.应用Stokes公式模拟了夹杂物沉降距离与静置时间的关系,分析了影响夹杂物沉降速度的因素.结果表明:在镁合金废料完全熔解后静置5～10 min,可以将熔体内夹杂物的含量降至0.5%以下,夹杂颗粒尺寸小于0.3 mm.234熔剂的精炼效果好于RJ-1熔剂,经234熔剂精炼后静置8 min,镁合金熔体中的夹杂物含量降至0.02%以下,夹杂颗粒尺寸小于10μm.夹杂物沉降速度与夹杂半径的平方、夹杂密度成正比,与镁合金液粘性系数及镁合金液密度和夹杂密度的比值成反比.     

混合稀土去除再生镁合金中的夹杂

在镁合金废料经过熔剂精炼后,依次添加0.05%～0.9%混合稀土,考察混合稀土对合金液净化效果的影响.结果表明:镁合金液中夹杂的体积分数由0.6%以上降低至0.2%以下.分析认为混合稀土的加入减少了合金液的氧化,反应形成了含稀土氯化物和氧化物的夹杂与镁合金液具有较大的密度差,有利于夹杂的沉降去除.因此,添加适量混合稀土可以起到净化镁合金液的作用.     

镁合金废料的回收

在镁合金零部件生产过程中,特别是在压力铸造生产中,产生出来的废料以及使用后报废的镁合金零件逐渐增多.出于成本和环境因素的考虑,必须对这与日俱增的镁合金废料进行有效回收.本文以生产占90%的镁合金零部件压力铸造为主线,介绍镁合金废料回收的经济分析,镁合金废料的来源和分类、现行回收技术的现状及发展趋势.并介绍香港生产力促进局和重庆硕龙科技公司最近研究开发的一种新型镁合金废料现场精炼回收系统.     

镁合金废料再生技术现状及发展趋势

随着镁合金产品应用范围逐渐扩大,生产过程中产生的废料以及使用后报废的镁合金零件逐渐增多,镁废料回收及再生以及相关环保问题愈来愈受到人们的重视。本文介绍了镁合金废料的分类、再生技术的现状及发展趋势,并讨论了再生过程中的质量要求与检测手段。     

镁合金废料的回收

在镁合金零部件生产过程中，特别是在压力铸造生产中，产生出来的废料以及使用后报废的镁合金零件逐渐增多。出于成本和环境因素的考虑，必须对这与日俱增的镁合金废料进行有效回收。本文以生产占90％的镁合金零部件压力铸造为主线，介绍镁合金废料回收的经济分析，镁合金废料的来源和分类、现行回收技术的现状及发展趋势。并介绍香港生产力促进局和重庆硕龙科技公司最近研究开发的一种新型镁合金废料现场精炼回收系统。     

镁合金废料的回收与利用

镁合金铸造及镁合金产品的广泛应用产生了大量的镁合金废料,本文讨论了镁合金废料的来源、分类、回收和再生技术,并分析了回收镁合金的质量及应用.     

镁合金废料的精炼效果研究

试验了熔剂组分的不同配比对AZ91镁合金废料精炼效果的影响,通过对精炼后得到的镁合金试样的金相显微观察,判断熔剂组分的最佳配比方案。阐述了熔剂对镁合金的精炼除夹杂机制。     

渗碳齿轮钢18CrNiMo7-6的疲劳性能及其影响因素

以18CrNiMo7-6齿轮钢为研究用基础钢,在传统真空脱气冶炼方式基础上,采用Nb微合金化和电渣重熔冶炼相结合获得一种对比试验钢,通过旋转弯曲疲劳试验表征了两种试验钢的疲劳性能,并利用显微组织、硬度分布、疲劳断口表征以及夹杂物分析等手段,探究了两种试验齿轮钢疲劳性能的影响因素。结果表明,采用电渣重熔方法冶炼并Nb微合金化的试验钢的疲劳极限较基础钢提高90 MPa,且相同载荷下寿命显著提高,渗碳层晶粒度由基础钢的7.5级细化至9级,而残留奥氏体含量的增加导致其表面硬度降低。通过Aspex夹杂物表征发现试验钢中夹杂物数量较基础钢大幅度降低,且硬质氧化物夹杂较少,与断口表征结果相一致。综合分析可知,晶粒细化和非金属夹杂物水平下降是提升试验钢疲劳性能的主要因素。     

制备工艺对再生高密度钨合金塑性的影响

对再生高密度钨合金塑性的提高作了较为深入地研究。结果表明：向再生合金原料粉末中加入适量的Ni，Fe元素进行成分调节可显著提高再生合金的塑性；对再生合金进行真空热处理可明显提高再生合金塑性，与热处理前相比，再生合金延伸率提高了约43．4％，截面收缩率提高了约33．9％。     

Recycling of AZ91 Mg alloy through consolidation of machined chips by extrusion and ECAP

AZ91 Mg alloy recycled by a solid state process and equal channel angular pressing (ECAP) exhibited a superior strength. The mechanical properties of AZ91 Mg alloy recycled from machined chips by extrusion at 623 K and ECAP at 573 K and 623 K were compared with those of the reference alloy which was produced from an as-received AZ91 Mg alloy block under the same conditions as the recycled alloy. The recycled specimens show a higher strength at room temperature than the reference alloy. The improvement of the tensile properties is attributed not only to the small grain size, but also to the dispersed oxide contaminants.     

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied. Various microstructural analyses were performed using the techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization. The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates. The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40:1. Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40:1. The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio. Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%, compared with those of the cast specimen.     

Influence of impurities on microstructure and mechanical properties of ZK60 magnesium alloy

The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy, scanning electron microscopy and tensile test. ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements. The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state. However, in the as-extruded state, reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa, while the elongations in the as-extruded alloys with different contents of impurities are almost the same. After T5 treatment, impurity content is found to have more obvious effect on the yield strength of ZK60 alloy. The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.     

Purification of metallurgical silicon using iron as impurity getter,part II: Extent of silicon purification

Purification of metallurgical grade silicon (MG-Si), using iron as the impurity getter has been investigated. The technique involves growing Si dendrites from an alloy of MG-Si with iron, followed by their separation using a gravity based technique and acid leaching. The effects of cooling rate of the alloy and the subsequent quenching temperature on the segregation of the impurities were studied. It was found that slow cooling of the alloy below the eutectic temperature causes an increase in the Si impurity concentration due to diffusion of the impurities from the alloy to the Si. Quenching the alloy from temperatures above the eutectic eliminated this effect, increasing the purity of the Si product. A significant reduction in the concentration of the major impurities was achieved, making the Si product a suitable feedstock for solar grade silicon generation. The concentrations, in ppmw, of some elements in the Si product are Al: 10, B: 2, Mn: 3, Ni: 3, Cr: 1, Fe: 1, P: 29. Other impurities including V, Ba, Li, Be, and Mg were all below 0.5 ppmw.     

过滤对高杂质含量的Al-12％Si合金组织和性能的影响

采用过滤器对电热法生产Al-30％Si粗合金配制的Al-12％Si合金进行了过滤除杂,研究了过滤对其微观组织及力学性能的影响.结果表明:该合金经过滤后能除去大部分Fe、Ca等杂质,使Fe相呈现出小块状或多面体状,球化趋势明显,消除了细长线状的Ca相,合金的力学性能得到明显改善,其抗拉强度已经接近纯Al配制合金.     

回炉料对K441合金性能及杂质元素含量的影响

通过采用真空感应熔炼法,对K441合金回炉料进行了四次熔炼,研究了回炉料对K441合金持久寿命、力学性能、杂质元素含量及微观组织形貌的影响.结果表明,经过四次回炉熔炼后合金的持久性能均满足标准的要求.合金的抗拉强度及塑性与新料合金相比变化幅度不大,但第四次回炉料合金的抗拉强度较高,这主要是由于Si元素的固溶强化作用所致.随回炉料合金回炉次数的增加,合金中的S元素含量降低,Mn含量变化幅度不大,P、Si元素含量增加.合金微观组织形貌观察表明,新料合金与回炉料合金中的碳化物均沿晶界分布,新料合金中晶粒内也存在部分碳化物.回炉料合金中的晶界存在杂质增加的现象.新料合金及回炉料合金中的γ'相数量相当,含量都较少,经多次回炉熔炼后合金中的γ'相尺寸减小.     

Characterization of plasma electrolytic oxide formed on AZ91 Mg alloy in KMnO4 electrolyte

The aim of this work is to investigate microstructure, corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO₄ contained solution. There are lots of closed pores that are filled with another oxide compound compared with the typical surface morphology with pore coated until 350 V of coating voltage. The thickness of oxide layer increases with increasing coating voltage. The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium permanganate consists of MgO and Mn₂O₃. Corrosion potential of the oxide layer on AZ91 Mg alloy obtained at different plasma electrolytic oxidation(PEO) reaction stages increases with increasing coating voltage. The corrosion resistance of AZ91 Mg alloy depends on the existence of the manganese oxide in the oxide layer. The inner barrier layer composed of the MgO and Mn₂O₃ may serve as diffusion barrier to enhance the corrosion resistance and may partially explain the excellent anti-corrosion performance in corrosion test. Nanohardness values increase with increasing coating voltage. The increase in the nanohardness may be due to the effect of manganese oxide in the oxide layer on AZ91 Mg alloy coated from electrolyte containing KMnO₄.     

镁合金废料再生技术

镁合金以其优越的性能正在得到广泛的应用,而镁合金废料的回用已成为镁工业可持续发展的关键环节.本文详细介绍了镁合金废料的来源与分类、再生方法、质量控制等,并对镁合金废料回用技术的发展进行展望.     

Effects of grain refinement on the microstructure,mechanical properties and reliability of AlSi7Cu3Mg gravity die cast cylinder heads

The effects of grain refinement on the microstructure and mechanical properties of a secondary AlSi7-Cu3Mg gravity die cast cylinder head are reported. Metallographic and image analysis techniques have been used to quantitatively examine the macro- and microstructural changes occurring with the addition of grain-refining agent. The results indicate that the AlTi5B1 addition produces a fine and uniform grain structure throughout the casting; this effect is more pronounced in the slowly solidified regions. The initial contents of Ti and B, which are present as impurity elements in the supplied secondary alloy ingots, are not sufficient to produce effective grain refinement. Under the present casting conditions, the combined addition of AlTi5B1 and Sr does not produce any reciprocal interaction or effect on primary α-Al and eutectic solidification. Grain refinement improves the mechanical properties of the as-cast AlSi7Cu3Mg alloy and produces higher Weibull moduli, thus increasing the reliability of the casting. For automotive structural components, this could be considered an increase in safety.