AZ91镁合金中Mg-Al连续析出相形貌的计算机模拟

建立了AZ91镁合金连续析出相的相场模型,研究了界面能各向异性和微观弹性应变能对析出相显微形貌的影响。结果表明:只考虑界面能各向异性,连续析出相端部为半圆形且为板条状形貌;只考虑微观弹性应变能,连续析出相呈现棱形形貌。两者综合考虑,析出相未出现明显的板条状特征,但端部呈现出平行四边形形状。

Mg-Al合金Mg_(17)Al_(12)连续析出相形貌的相场模拟

基于KKS相场模型模拟了Mg-Al合金Mg_(17)Al_(12)单个连续析出相的形貌演化.相场模型中,各相自由能及化学势由Thermo-Calc热力学计算软件计算.构造各向异性函数时考虑了界面能各向异性的影响,基于Khachaturyan微观弹性应变能理论考虑了微观弹性应变能的影响.结果表明:仅考虑界面能各向异性不考虑微观弹性应变能,析出相呈板条状形貌;仅考虑微观弹性应变能不考虑界面能各向异性,析出相呈菱形:综合考虑界面能各向异性和微观弹性应变能,析出相呈板条状形貌,端部呈平行四边形,此形貌特征与实验观察结果吻合;界面能各向异性决定析出相的板条状形貌特征,微观弹性应变能导致端部产生平行四边形特征.

Modulation of microstructure and properties of Cu−Ni−Sn alloy by addition of trace Ti

The segregation of Sn and discontinuous precipitation at grain boundaries are detrimental to the strength,ductility,and machinability of the Cu−Ni−Sn alloy.A strategy to solve the above problems is multi-component composition design by introducing strong enthalpic interaction element.In this work,a series of Cu_(80)Ni_(15)Sn_(5−x)Ti_(x)(at.%)alloys were designed by cluster-plus-glue-atom model,and the effects of Ti content on the microstructure and properties of the alloys were systematically investigated using TEM and other analysis methods.The results demonstrate that Ti can effectively inhibit the segregation and discontinuous precipitation while promoting continuous precipitation to improve the high-temperature stability of the alloys.As the Ti content increases,the distribution of Ti changes from uniform distribution to predominant precipitation.The hardness and conductivity of the alloy exceed those of the C72900(Cu−15Ni−8Sn(wt.%))commercial alloy and the Cu_(80)Ni_(15)Sn_(5)(at.%)reference alloy when Ti is in the solution state.

轨道交通用7003铝合金型材失效行为分析

采用金相、扫描电镜和透射电镜观察以及慢应变速率拉伸应力腐蚀实验等分析测试方法对轨道交通用7003铝合金型材的失效原因进行分析。研究结果表明:型材失效件的裂纹为沿晶扩展,且有支裂纹向外扩展;失效件断口形貌呈冰糖块状花样特征,断口表面附集着铝、锌的氧化物,还有少量氯化物和硫化物,经分析失效型材的裂纹是由应力腐蚀导致的沿晶脆性断裂。型材试样在30 g/L Na Cl+10 m L/L HCl腐蚀溶液中的抗拉强度为181.5MPa,断裂时间为5.1 h,在空气中的抗拉强度为320.3 MPa,断裂时间为27.7 h,试样的应力腐蚀敏感指数(ISSRT)为0.46。晶界析出相尺寸较小、密度大,且呈链状连续分布,在腐蚀过程中,晶界连续析出相易成为阳极腐蚀通道,是较高的应力腐蚀敏感性的主要原因。

热处理对大规格等温模锻AZ80-Ag镁合金机匣显微组织和拉伸力学性能的影响

研究大规格等温模锻AZ80−Ag镁合金机匣在不同热处理条件下的组织演变和拉伸力学性能。采用扫描电镜和电子背散射衍射对合金的显微组织进行表征,并测试其在室温、120和150℃下的拉伸力学性能。结果表明,室温下强化作用更强的不连续析出相在T5样品中的面积分数高于T6样品的面积分数。因此,T5样品的析出强化作用更强,室温抗拉强度最高。但随着温度的升高,T5样品的抗拉强度迅速下降,在150℃时低于T6样品甚至锻造态样品的抗拉强度。这是由于不连续析出相的抗高温软化能力低于连续析出相的抗高温软化能力。

Continuous cooling precipitation diagram of cast aluminium alloy Al-7Si-0.3Mg

The precipitation behaviour during quenching of cast Al-7Si-0.3Mg aluminium alloy was investigated by DSC in the cooling rate range of 0.01 K/s to 3 K/s and by quenching dilatometry for higher rates. Two main precipitation reactions were observed during cooling, a high temperature reaction starting almost directly with quenching from 540℃ and a low temperature reaction starting at about 400℃. Quenching with 3 K/s already significantly suppresses precipitation during quenching. Hardness after T6 ageing increases with increasing quenching rate, due to the increasing content of supersaturated solid solution. By dilatometry and hardness results the critical cooling rate can be estimated as about 60 K/s. Quenched Al-7Si-0.3Mg microstructures have been investigated by light microscopy. The microstructures consist of an aluminium-silicon eutectic structure, aluminium solid solution dendrites and precipitates inside the aluminium dendrites, depending on quenching rate.

预变形对Cu-6Ag合金时效析出及性能的影响

Cu-Ag合金是具有重要应用前景的高强高导合金,其形变加工和热处理工艺的改进对性能的进一步提高具有重要作用,但热处理前预形变的作用一直未受重视。本工作通过XRD物相分析、维氏硬度、电导率、金相显微镜和扫描电镜等方法,研究了预变形对固溶+时效处理的Cu-6Ag合金组织和性能的影响。结果表明,预变形促使Cu-6Ag合金发生再结晶,晶粒尺寸明显减小。同时,预变形降低了时效处理后Cu-6Ag合金的固溶量。预变形+时效处理的样品与未进行预变形的样品中均观察到非连续性析出相。预变形合金中的非连续析出相间距更小,为95±9.5 nm。预变形合金的硬度(HV)稍低于未预变形合金,为840.8 MPa,导电率与未预变形合金基本持平,为90.3%IACS。