6061铝合金材料常数的研究

通过热压缩试验,研究了6061铝合金材料的流动应力与温度、应变速率和应变之间的关系。根据试验数据,采用一元线性回归方法,确定了该材料的常数,如:激活能Q、应力指数n、应力水平参数α和结构因子A。研究表明,高温压缩变形时,6061铝合金的软化中动态回复是主要的;6061铝合金是正应变敏感材料。     

反挤压对SiCw/6061力学性能影响的实验研究

以挤压工艺对SiCw/6061复合材料力学性能的影响为研究目标,通过改变挤压温度、挤压比以及凸模中心锥角等工艺参数,系统分析了挤压铸造制备的SiCw/6061复合材料反挤压变形前后强度、塑性及硬度的变化规律.研究表明,挤压变形可以有效地提升复合材料试件的各项力学性能指标;随着挤压温度的升高,试件的屈服强度、抗拉强度均呈现升高的变化趋势,延伸率先显著增大而后略有减小,硬度则呈现下降的趋势;随着挤压比的增加,试件的强度、塑性及硬度均呈现上升趋势;随着凸模中心锥角的增大,试件的屈服强度、抗拉强度均呈现先升高后下降的趋势,延伸率及硬度则随着锥角的增加始终呈上升趋势.     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

热处理对SiCp/6061Al基复合材料等离子弧焊接头性能的影响

热处理对SiCp/6061Al基复合材料等离子弧原位焊接接头组织与性能的影响较为明显,固溶处理 时效与退火相比,前者对接头的改善作用更佳.经500 ℃固溶处理2 h 12 h时效热处理后,接头组织得到良好的改善,细长的Al3Ti相变为短小棒状,消除了晶间偏析,组织更加均匀;热影响区组织中晶粒均得到比较明显的细化,比较接近母材晶粒的大小,焊接接头强度较未热处理时有了较大提高,达到245 MPa.     

薄壁6061铝合金TIG焊接结构强度研究

焊缝强度是影响薄壁承压容器整体强度的关键因素,为研究保证其焊缝强度的焊接及热处理工艺路线,采用TIG方法对薄壁6061铝合金材料进行了焊接,焊后采用了固溶加人工时效的热处理方式。通过拉伸试验对焊缝的强度进行研究,确定了合适的焊接参数和热处理工艺,分析了焊缝缺陷的产生原因和解决办法。     

6061合金时效及停放效应的工艺探讨

6061铝合金挤压型材经在线淬火处理后,在(175士5)℃、保温8h的时效制度下进行人工时效时,发现停放时间对人工时效后型材的力学性能有较大影响.停放时间在3h之内,经人工时效处理后,型材的强度较高,但延伸率偏低;在停放时间为8～20 h时,经人工时效处理后强度下降较大.根据客户对产品性能的不同要求,可选择适当的停放时...     

6061铝合金断裂机理的原位拉伸研究

用SEM-520原位拉伸试验对不同应力状态下6061铝合金试件的断裂过程进行研究.结果表明,不同应力状态下的铝合金试样在拉伸过程中其表面均产生了大量的滑移带,但断裂机理不同.随着三轴应力度的降低,断裂从韧窝聚合型混合剪切机制向纯剪切断裂机制过渡,试件断口也由韧窝断裂模式向剪切断裂模式演变;6061铝合金晶界处为最薄弱环节,微裂纹形核于晶界,随载荷的增加,微裂纹长大和扩展.微裂纹之间通过扩展或剪切而连接导致试样断裂;试样最小断面上的三轴应力度越小,试样断口的两个面上韧窝的取向就越明显,断口越光滑.     

LZ50车轴“发纹”缺陷分析及控制措施

本文研究了LZ50车轴“发纹”产生的机理,分析了钢中氧化铝类夹杂、铝、氮的质量分数等因素与发纹的关系,提出了具体的控制措施。     

Investigation of computer hardware failure due to corrosion

Abstract

Failure analysis was conducted on two failed electronic cardsfrom the Computer Center of the Kuwait Institute for Scientific Research. The results of the elemental analysis indicated that the corrosion product film found on contact pins and soldered through holes was composed of copper and sulphur compounds. Chemical analysis of the air in the computer room indicated a high level of nitrogen oxide (up to 300 ppb), whereas other gases such as H²S and SO² were below the detectahle limits (100 and 200 ppb respectively) of the analytical technique used. It was concluded that the initial high relative humidity ( ～ 75%) had synergised with the strongly oxidising nitrogen oxide and H²S and/or SO² to bring about the corrosion of copper substrate in ‘bare spots’ or gaps in the soldered contacts, causing card failure. Other factors, such as galvanic coupling of the copper substrate with nickel, silver, and gold plates, and the relatively high local temperature, may have accelerated the corrosion process. A decrease in the relative humidity to the optimum value of 45% did not obviate card failure. It was concluded that efficient air filters should be utilised in the computer environment, as electronic equipment can be damaged by levels of pollutant gases 10 times lower than those cited for human safety requirements.     

Hardness and microstructural developments of spray formed aluminium alloys with high Mg2Si content during hot extrusion and heat treatment

Abstract

Spray forming offers the possibility of producing alloys with very fine, homogeneous microstructures. Even materials with high contents of intermetallic precipitates, which cannot be produced by casting because of the high solidification rates required, can be distributed homogeneously. Alloying aluminium with high contents of Mg and Si (>20 wt-%Mg₂Si) gives an increase in stiffness plus a significant reduction in density, but a very fine distribution of the Mg₂Si particles in the aluminium matrix is required. Therefore, such alloys are commonly produced by spray forming. Post-spraying processes such as forming and heat treatment are generally carried out to optimise properties. To examine the microstructure and hardness as a result of subsequent processing, aluminium alloys with high Mg₂Si content (22–30 wt-%) have been produced under a variety of spray forming conditions. The duration and temperature of heating before extrusion were varied. In addition, some specimens were preheated without extrusion. The influence of subsequent heat treatment was investigated by varying the age hardening parameters. Hardness measurements were conducted and the distribution and size of the precipitates were evaluated by light microscopy. Image analysis was used to study the coarsening behaviour of primary Mg₂Si. The results indicate that the subsequent processing conditions have a strong influence on the microstructure and hardness of the material. Further, a significant dependence of coarsening rate during subsequent processing on the initial state of the material after spray forming was observed. Knowledge of correlations between process parameters and microstructural development offers the possibility of optimising the hot extrusion and heat treatment parameters for high Mg₂Si containing aluminium alloys.