铝合金材料压铸加工中典型缺陷分析及解决措施

以摩托车气缸体的压铸加工为例 ,介绍了铝合金材料在压铸生产加工过程中较易产生的气孔、缩孔、欠铸、凹陷等典型缺陷 ,并结合压铸机的工作状态、模具结构的合理性、压铸工艺参数的选用、合金熔炼的质量以及压铸操作等多种因素 ,分析了各种缺陷的形成原因以及消除缺陷的相应措施     

The effect of precipitation of Mg2Al3 and of MnAl6 on texture evolution during isothermal annealing and subsequently on formability of CC AA5182 Al alloy

Continuous cast (CC) AA5182 Al alloy with the precipitation of Mg₂Al₃ and of MnAl₆ was cold rolled to 70% reduction and then isothermally annealed in a salt bath at three temperatures (316, 343, and 371 °C) for different times. Texture evolution during recrystallization was investigated. It was found that the recrystallization textures of the material with intense Mg₂Al₃ precipitation along the grain boundaries exhibited weaker Cube, Goss and R/β fiber components than those of the material with the more uniform fine MnAl₆ precipitates. The opposite was true in the cold rolled condition, i.e. the material with MnAl₆ precipitation had weaker Cube, Goss, and R/β fiber components in the cold rolled condition than the material with intense Mg₂Al₃ precipitation. Thus, recrystallization textures of material with Mg₂Al₃ precipitation were weaker than material with MnAl₆ precipitation. This is due to the fact that large Mg₂Al₃ particles favor the nucleation of randomly oriented grains. When subjected to formability tests, the material with prior Mg₂Al₃ precipitation displayed a lower anisotropy in tensile yield strength, ultimate tensile strength, elongation, and strain hardening exponent than material with prior MnAl₆ precipitation. This is in accord with the texture results which indicated that the recrystallization textures of material with an initial Mg₂Al₃ precipitation were closer to those of a perfectly random sample than those of material with an initial MnAl₆ precipitation. On the other hand, the elongation and Olsen values were lower and the surface quality after bending tests was worse for material with Mg₂Al₃ precipitation. This is due to the non-uniform distribution of Mg₂Al₃ particles which precipitated primarily along the grain boundaries and caused an earlier formation and coalescence of the microvoids around the grain boundary precipitates. The forming limit diagrams (FLD) correlated well with the tensile, Olsen and bending results.     

High-Temperature Strength of Niobium Alloy 5VMTs with a Silicide-Ceramic Coating. Part 1. Short-Term Strength Characteristics

Experimental data on the short-term strength and plasticity of niobium alloy 5VMTs of the system Nb–W–Mo–Zr in its initial state, after annealing, and with a silicide-ceramic protective coating obtained by testing in vacuum, an inert atmosphere, and in air in the temperature range from 290 to 2270 K are analyzed. The process of microcrack initiation and propagation in the protective coating and matrix is investigated in high-temperature static tension. The limiting plastic strain values have been established at which the composite retains its load-carrying capacity in high- temperature aggressive and oxidizing gas atmospheres.     

Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.     

BT20钛合金低温铣削试验研究

为改善钛合金工件的加工表面质量,进行了低温铣削钛合金试验,并得出了合理的切削用量。     

基于ABAQUS软件的微米级金属材料性能研究

为工程实践中迫切需要解决微米和亚微米量级的设计与制造问题,文章中运用MSG塑性理论利用Abaqus软件对铝合金的强度及均匀延伸率进行了比较系统的研究;运用有限单元法分析了MSG应变梯度本构方程和经典的弹塑性本构方程对不同晶粒尺寸的铝合金的应力应变关系;模拟不同晶粒尺寸的铝合金的强度及均匀延伸率。结果表明随着晶粒尺寸的减小,屈服强度、应变硬化明显增加,延伸率却往往越小。对于该问题的研究探索,将是解决材料强度与均匀伸长率这对矛盾体的问题关键,同时,为科研工作者提供了新方法和新途径。     

二甲酚橙褪色光度法测定水样中的镁

本文作者研究了利用褪色光度法测量水样中微量镁的方法。结果表明:在一定条件下,方法的摩尔吸光系数为1 68×105L·mol-1·cm-1,精密度(RSD)为1 6%,回收率为93%～101%。     

轴向均布荷载压杆稳定问题的重心插值配点法

用重心插值配点法对轴向均布荷载下压杆稳定问题进行了研究。采用重心Lagrange插值多项式建立未知函数的微分矩阵,采用配点法将压杆稳定问题的控制方程表示为代数方程组。通过求解代数方程组系数矩阵的特征值和特征向量,得到了精度很高的后屈曲挠度数值和临界载荷数值。实例证明,这种方法原理简单,易于程序实现。     

镁合金表面防护研究进展

文章综述了镁合金的几种表面防护技术:化学处理、阳极氧化、微弧氧电镀、物理气象沉积(PVD)等,并提出了今后的研究发展方向。     

Al—Zn—Mg—Cu合金的超塑性变形力学行为

介绍了一种新的超塑性处理工艺,采用简单的预处理工艺结合升温拉伸,可以使合金获得优异的超塑性,轧制形变组织在拉伸过程中发生动态再结晶,形成细晶组织并赋予合金优异的超塑性。