A356.2铸造铝合金生产中Si偏析的影响

论述了铸造铝合金生产中不同时间和状态下采样对Si偏析的影响及Si偏析对产品的影响,并应用于指导生产实际。     

A356.2低压铸造铝合金车轮中Si偏析对产品质量的影响

A356.2低压铸造铝合金车轮通常会存在化学成分偏析的情况,通过对缺陷样件化学成分、金相组织等研究分析,发现存在偏析问题的样件化学成分、晶粒尺寸、产品外观样貌均存在异常。铸造铝合金车轮的成分偏析主要就是Si元素偏析,所以在铝合金车轮低压铸造过程中,合理的低压铸造工艺设计是解决其化学成分偏析、提高产品外观质量的最有效途径之一。     

A356．2铸造铝合金生产中采样状态和采样时机对Si偏析的影响

本文通过试验摸索,找出规律,论述了铸造铝合金生产中不同时间和状态下采样对Si偏析的影响,并应用于指导生产实际。     

样模的外观结构对A356.2铸造铝合金中Si偏析的影响

介绍了A356.2铸造铝合金生产过程中,采用不同的样模做化学成分取样分析时,Si的偏析情况。结果显示,采用改进后的样模,液态样的分析数据结果能更准确的代表成品样的分析结果,从而有效控制A356.2铸造铝合金的生产过程。     

间接挤压铸造工艺参数对铝合金中Si偏析的影响

研究间接挤压铸造工艺条件下,浇注温度、挤压压力、挤压速度、冷却速度及参数间的交互作用对6066铝合金中Si元素的偏析影响规律.以凝固后零件热节位置硅的质量分数与合金初始硅的质量分数的差值定量表征偏析程度,采用考虑一级交互作用的四因素两水平正交设计,研究间接挤压条件下硅的偏析现象.结果发现:浇注温度、挤压压力、挤压速度和冷却速度对硅偏析都有影响,其中浇注温度是影响最显著的因素.随着浇注温度的升高,铝合金中Si偏析程度减小.挤压压力和挤压速度对硅偏析的影响次之,但两者的影响趋势相反;模具冷却能力的影响程度与挤压压力和挤压速度的交互作用的影响程度相似,铜模套(高冷速)比钢模套(低冷速)的硅偏析程度要轻.间接挤压铸造条件下,工件热节位置可以出现硅的负偏析.      

浅谈铝镁合金光谱分析镁含量偏差的措施

在铝镁合金工业化生产过程中,镁元素受其物理化学特性影响,铸造过程中极易产生偏析,偏析造成了铝合金产品的化学成分波动。本文针对5052铝合金中镁偏析进行了试验分析,并对检测样品取样、检测前预处理方式等方面提出了改进措施。     

挤压铸造零件沿流程方向的成分偏析及组织偏聚

采用挤压铸造(液态模锻)工艺制备了A357铝合金螺旋线试件,使用化学成分分析和金相分析方法研究了流程长度对合金成分偏析及组织偏聚的影响.结果表明:在沿流程方向上,流程的开始端和流程末端的Si元素和Mg元素含量大于流程中段的含量.合金的初始α晶粒尺寸随着流程长度的增加先增大后变小.初生固相率随着流程长度的增大呈现波动变化.造成流程成分偏析和组织变化的原因是在挤压铸造凝固阶段中补缩液相的强迫运动.      

半连续铸锭缺陷及其预防措施（续10）

4 铸锭的表面缺陷和几何缺陷直接水冷半连续铸造的变形铝合金铸锭,其表面通常有偏析瘤(偏析浮出物、偏析     

冷冻铸造A356铝合金微观组织分析

基于数字化无模冷冻铸造精密成形技术实现了冷冻砂型的快速成形,对其浇注A356高温铝合金获得冷冻铸造平板试件。采用电子探针显微分析技术对冷冻铸造和树脂砂型铸造铸件微量元素的分布进行了表征,同时对冷冻铸造和树脂砂型铸造铸件断裂形貌进行了分析。结果表明,冷冻铸造Si元素在铝基体相中的溶解度较树脂砂型铸造显著提高,冷冻铸造较树脂砂型铸造试件中Mg元素分布均匀,树脂砂型铸造试件中出现较多的Mg元素成分偏析区;冷冻铸造试件断裂方式为韧性和脆性的混合断裂模式,树脂砂型铸造试件的断裂形貌为解理台阶破坏形貌和长方状的撕裂结构形貌,合金偏向于脆性断裂。      

A356铝合金轮毂Si偏析现象及力学性能

采用扫描电镜、金相显微和拉伸实验等分析了低压铸造A356轮毂的组织，建立了Si偏析现象的表征方法，并探讨了铸件SDAS值和Si颗粒平均面积对其力学性能的影响。结果表明:采用共晶面积分数、Si颗粒平均面积和长径比可以很好地表征Si偏析程度; 轮毂轮辐中部R角处共晶面积分数、Si颗粒平均面积、长径比和SDAS值分别为34.83%、11.33 μm2、2.46和56.89 μm，相应的UTS、YS和EL值分别为229.02、152.67 MPa和5.34%，轮毂Si偏析程度越高的部位，其力学性能也越差。在分析铸件拉伸性能时，应综合考虑SDAS与Si偏析的影响。并且给出了解决Si偏析问题的具体措施。      

改良铸造铝硅镁合金的成分优化设计

以传统铸造铝硅镁合金为基础,对改良铸造铝硅镁合金的成分优化设计进行了研究。研究结果表明,改良铸造铝硅镁合金的成分设计合理,合金不但具有良好的常温和高温力学性能,而且还具有优良的铸造性能。     

Development of a novel hypereutectic aluminum-siliconmagnesium alloy for die casting

A novel hypereutectic die casting Al-Si-Mg alloy with relatively high Mg content was developed. The optimized microstructure of the alloy is characterized by a fine dispersion of eutectic Si and Mg₂Si particles in an α-Al matrix which is devoid of primary silicon particles. Of the several modifiers used to refine the coarse morphology of the Mg₂Si particles, an optimum combination of strontium and misch metal yielded the best results. The refined microstructure after a standard T6 heat treatment accounts for the enhanced room temperature tensile properties of castings made from this alloy.     

Effect of silicon particles on the fatigue crack growth characteristics of Al-12 Wt Pct Si-0.35 Wt Pct Mg-(0 to 0.02) Wt Pct Sr casting alloys

Fatigue crack growth (FCG) characteristics and mechanisms in Al-Si-Mg eutectic casting alloys containing 0.35 wt pct Mg and 0 to 0.02 wt pct Sr were investigated as a function of stress ratio,R, stress-intensity-factor range, ΔK, and silicon (Si) particle size. The fatigue crack propagation behavior was compared with that observed in commercial casting alloy A356. At the same applied ΔK level, the crack growth rate was found to increase with increasing stress ratio and Si particle size. Modified (fine Si morphology) and A356 alloys showed better FCG resistance than the unmodified (coarse Si morphology) ones, for a constant applied ΔK, due to increased closure. The effects of roughness-induced and plasticity-induced crack closures, crack branching, and crack meandering on the fatigue crack propagation observed in these alloys have been discussed. The fatigue crack propagation path is found to be dependent on the Si particle characteristics. The mechanisms of silicon particle decohesion and cracking are also discussed. Formerly Research Associate, Département des Sciences Appliquées, Université du Québec à Chicoutimi     

Localized Recrystallization in Cast Al-Si-Mg Alloy during Solution Heat Treatment: Dilatometric and Calorimetric Studies

During heat treatment, the work piece experiences a range of heating rates depending upon the sizes and types of furnace. When the Al-Si-Mg cast alloy is heated to the solutionizing temperature, recrystallization takes place during the ramp-up stage. The effect of heating rate on recrystallization in the A356 (Al-Si-Mg) alloy was studied using dilatometric and calorimetric methods. Recrystallization in as-cast Al-Si alloys is a localized event and is confined to the elasto-plastic zone surrounding the eutectic Si phase; there is no evidence of recrystallization in the center of the primary Al dendritic region. The size of the elasto-plastic zone is of the same order of magnitude as the Si particles, and recrystallized grains are observed in the elasto-plastic region near the Si particles. The coefficient of thermal expansion of Al is an order of magnitude greater than Si, and thermal stresses are generated due to the thermal mismatch between the Al phase and Si particles providing the driving force for recrystallization. In contrast, recrystallization in Al wrought alloy (7075) occurs uniformly throughout the matrix, stored energy due to cold work being the driving force for recrystallization in wrought alloys. The activation energy for recrystallization in as-cast A356 alloy is 127 KJ/mole. At a slow heating rate of 4.3 K/min, creep occurs during the heating stage of solution heat treatment. However, creep does not occur in samples heated at higher heating rates, namely, 520, 130, and 17.3 K/min.     

原位统计分布分析技术分析不同中低合金钢连铸板坯横截面上碳、硅、锰、磷、硫、铌、钛、钒

采用金属原位统计分布分析（OPA）技术考察了不同生产工艺条件下不同厚度的中低合金钢连铸板坯横截面上C、Si、Mn、P、S、Nb、Ti、V等元素的分布、富集及中心偏析形态。观察并描述了几种典型的中心偏析形式,如断续的、连续的以及正负偏析呈交错分布状等;发现大多元素的中心偏析模式相对固定,即在沿拉速方向一定厚度范围内具有稳定性;给出了最大偏析度、统计偏析度等定量表征元素分布状态的原位技术特征值;讨论了各元素在板坯中形成偏析的难易程度及常见的分布模式。硫元素的偏析分析结果和传统分析硫偏析的方法-硫印也基本一致。研究表明,原位统计分布分析技术能有效地应用于较宽含量范围内、不同厚度尺寸的中低合金钢板坯的成分分布分析和偏析分析,且其分析结果具有很好的重复性和可靠性。     

Effects of Be and Fe additions on the microstructure and mechanical properties of A357.0 alloys

A357 hypoeutectic alloy is a heat-treatable Al-Si-Mg system with a nominal composition of Al-7 pct Si and about 0.6 pct Mg have widespreaded applications, especially in the aerospace and automotive industries. The purpose of this study was to determine the influences of Be and Fe content on the microstructure and mechanical properties of A357.0 alloys. Distinct morphologies were discerned between Be-containing and Be-free alloys. The Be-free alloys contain larger amount of iron-bearing phases with Mg than in Be-containing alloys. The addition of Be can change the plateletlike structure of iron-bearing phases to a comparatively harmless round nodular form. Also, the amounts of iron-rich phases are significantly lower and the silicon particles are smaller and more spherical in the Be-containing alloys. Small amounts of Be in A357.0 caused significant increases in the precipitation kinetics of Mg₂Si. It was found that the addition of Be lowers the ternary and binary eutectic melting point. The amount of Mg available to form the major strengthening phase Mg₂Si is increased promoting the tensile strength of A357.0 casting. The tensile properties were improved with decreasing Fe content and the addition of Be. The effect is more apparent in the higher Fe alloys than that in the lower Fe alloys.     

铸造黄铜的原位统计分布分析

采用金属原位分析仪实现了对铸造黄铜ZHPb59-1的大面积扫描,利用原位统计分布分析技术分析了合金中添加元素Zn、P、Mn、Al、Si、Fe、Pb、Ti、B的分布状况,以期能为铜合金行业提供一种快速的表面元素分布分析方法。通过原位扫描技术能快速得到各元素的直观分布图、最大偏析度、最大偏析位置和统计偏析度。研究发现,原位分析得到Zn、P、Mn的分布及对组织影响的结果和金相结果有良好的对应;通过二维成分分布图和三维成分分布图可看出Al、Si、Fe的分布较为均匀。由原位统计分布可推测,Pb存在大量的夹杂相,而P弥散在整个合金中;Ti、B作为主要的变质剂,存在明显的偏析。此外,Cu、P夹杂的原位统计结果与扫描电镜和能谱的结果对应良好。