热变形对喷射成形7055铝合金挤压板微观组织的影响

通过单道次热压缩实验和Deform有限元模拟相结合的方法,研究了喷射成形7055铝合金挤压板在300~450℃、0.01~25 s^(−1)范围内的热变形行为。结合热压缩实验获得的热加工图、Deform模拟热压缩过程获得的真实应变和损伤分布以及计算出的几何必需位错(GND)和形变储能,综合分析了合金在热变形过程中的微观组织演变。结果表明:安全加工区位于低应变速率区,其中高温低应变速率区域(400~450℃,0.01~1.0 s^(−1))为其最适宜热加工条件,在该区域热加工后,功率耗散系数(η值)最大,损伤值最低。失稳区集中在高应变速率区域(即1.0~25 s^(−1)区间内),该区域具有最大的损伤值并易于开裂。此外,针对因挤压板在失稳区热加工后表层和中心样品在后续470℃/2 h固溶处理过程中出现的粗晶和晶粒异常长大问题,设计了在热变形前进行慢速升温长时热处理的工艺方案,并讨论了相关的再结晶行为。该热处理制度可以有效降低挤压板中的残余位错密度和形变储能,且在慢速升温过程中析出的大量Al3Zr粒子具有钉扎晶界、降低界面迁移率和阻碍位错运动的作用,从而抑制了热变形后板材在固溶处理过程中的静态再结晶。

预处理工艺对双辊铸轧3003铝合金再结晶行为的影响

对双辊铸轧3003铝合金板材进行了3种预处理退火,研究不同预处理工艺下的冷轧板材在380～500℃退火时晶粒组织和再结晶织构的变化规律。结果表明:最优化预处理工艺为610℃/12h+460℃/12h,高温阶段第二相尺寸发生粗化,低温阶段基体中Mn的过饱和固溶度显著降低,两者均有利于提高后续退火时的再结晶形核率。500℃退火时,在粗大第二相的附近产生了粒子诱发形核机制,降低了再结晶织构强度;并且退火时几乎不存在析出,析出相对再结晶形核的抑制作用甚微,从而得到了晶粒细小、织构弱的再结晶组织。

异种铝合金搅拌摩擦焊接头的显微组织、力学及腐蚀性能

采用3种焊接速度(60、100和240 mm/min)对5 mm厚2024和7075铝合金板材进行搅拌摩擦对接焊试验,利用电子背散射衍射(EBSD)、硬度测试、拉伸试验、扫描电镜和极化曲线测试对2024-7075异种铝合金搅拌摩擦焊接头的显微组织、力学性能及腐蚀行为进行了研究。结果表明:接头焊核区发生动态再结晶形成细小的等轴晶。沿板厚方向从轴肩区到底部区的平均晶粒尺寸依次减小,且焊核区不同位置处的平均晶粒尺寸均随着焊接速度的增加而减小。异种接头焊核区不同位置形成不同类型的剪切织构,其类型随焊接速度的改变而变化。接头焊核区硬度呈现"W"型分布趋势,且低于母材硬度。较低硬度值区域位于热影响区,随着焊接速度的降低,各区硬度值呈现下降的趋势。接头强度随着焊接速度的增加而升高,焊接效率达到90.3%。与母材相比,焊接接头焊核区的耐蚀性最差,这主要是由于异种焊接接头焊核区发生了显著的电偶腐蚀,导致较高的腐蚀电流密度。

不同冷轧路径下ZX21镁合金板材织构及力学性能调控机理

研究轧制路径对ZX21镁合金板材织构分布和屈服各向异性的影响。结果表明:单向轧制板材形变织构为双峰基面织构,退火后呈现出垂直于冷轧方向分布的非基面双峰的织构特征。再结晶织构的分布与晶粒的定向形核和选择性长大有关,多向轧制可弱化晶粒取向分布的方向性,其晶粒尺寸相比单向轧制有所减小,退火后形成均匀分布的圈状织构,大幅降低沿轧面各个方向拉伸时基面滑移的施密特因子差异,改善板面内的力学性能各向异性,提高板材的成型性。

7B04包铝复合板热变形行为及其对组织演变的影响

利用热模拟实验研究7B04包铝复合板在变形温度为380~450℃和应变速率为0.1~30 s^(-1)的热压缩性能,结果表明:随着真应变的增加,热加工图失稳区逐渐向高应变速率区域扩展。最适宜的热加工区域为:温度380~410℃,应变速率5~30 s^(-1)。采用EBSD技术对变形后的组织进行表征,结果表明:随着温度的增加和应变速率的降低,再结晶晶粒趋向于晶界平直化及晶界取向差逐渐增加的方向演变。包铝层在变形过程中主要发生连续动态再结晶,而7B04基体中同时存在不连续动态再结晶、连续动态再结晶(含几何动态再结晶)。材料最佳的热变形温度为410℃和应变速率10 s^(-1),此时7B04基体和包铝层的晶粒尺寸均保持在较小的范围内。

Effect of ageing temperature on precipitation of A1-Cu-Li-Mn-Zr alloy

The precipitation behaviors of an A1-Cu-Li-Mn-Zr alloy at different ageing temperatures （120, 160 and 200 ~C） were investigated using Vickers hardness measurements and transmission electron microscopy （TEM） characterization. Age hardening curves show an increase in precipitation kinetics with increasing ageing temperature. The results of TEM show that for the samples peak aged at 120 ~C, the amount of g＇ （A13Li）, GP zones/0＇ （A12Cu） and Z （A15Cu6Li2） phases is obviously higher than that of T1 （A12CuLi） precipitates; while the samples peak aged at 160 and 200 ~C are usually dominated by T1 phase with a minor fraction of GP zones/0＇ and g＇, and the Z phase almost does not form. In addition, quantitative analysis on the T1 platelets demonstrates that the samples peak aged at 200 ~C have larger plate diameter and smaller area fraction of T1, as compared to the samples peak aged at 160 ~C. Correspondingly, the possible reasons for such phenomena are discussed.

Effect of platform temperature on microstructure and corrosion resistance of selective laser melted Al-Mg-Sc alloy plate

The Al-3.40Mg-1.08Sc alloy plates were manufactured by selective laser melting(SLM) at platform temperatures of 35 ℃ and 200 ℃, respectively, and the corrosion performance of them was studied along height direction. The results show that the corrosion resistance of the alloy plate built at platform temperature of 35 ℃ along height direction is basically the same due to a uniform microstructure;While the corrosion resistance of the alloy plate built at platform temperature of 200 ℃ along height direction is different. The evolution of microstructure and the distribution of secondary phases are investigated, and the results show that the Cu-rich phases in alloy play a key role on corrosion performance. At higher platform temperature, the cooling rate is relative slow and a certain degree of in situ ageing leads to the significantly different distribution of Cu-rich phases along grain boundary. Specimens built at the platform temperature of 200 ℃ are inclined to locate at the crossed grain boundary, rather than continuous segregation of Cu-rich phases along grain boundary that is built at platform temperature of 35 ℃. Therefore, the corrosion resistance of Al-3.40Mg-1.08Sc alloy plate manufactured at platform temperature of 200 ℃ is higher, and presents a gradually decreasing trend along height direction.

Effect of pre-recovery on subsequent recrystallization kinetics in moderately deformed and supersaturated Al–Mn alloys

The effect of pre-recovery on the recrystallization kinetics of a supersaturated Al–Mn alloy annealed at 530°C was investigated.The results show that the pre-recovery treatment can lead to faster recrystallization kinetics at the initial stage but cause sluggish recrystallization at the later stage.This different recrystallization behavior is explained by the formation of precipitates-free zones and the consumption of driving force during the pre-recovery treatment.The promoted recrystallization at the early stage can be interpreted by the promotion of recrystallization nucleation through sub-grain growth to a critical size inside precipitates-free zones.A simple model is presented to describe the nucleation of recrystallization with pre-recovery treatment in the supersaturated Al–Mn alloys.

Micro porosity and its effect on fatigue performance of 7050 aluminum thick plates

Micro porosity in aluminum alloys may contribute to fatigue life degradation, which can largely limit the application of alloys. Therefore, the fatigue life of a commercial 7050-T7451 thick plate and an experimental plate with different porosities was compared in this study. The X-ray computed tomography(XCT) was utilized to characterize the size, number density and spatial distribution of porosity inside various samples, and the fracture surface of fatigued specimens was compared by using scanning electron microscope(SEM). The results showed that the fatigue cracks prefer to initiate from constituent particles in the commercial alloy. Whereas the micro porosity is the predominant site for crack nucleation and subsequent failure in the experimental one. The presence of micro porosity in experimental7050-T7451 thick plate may reduce the fatigue life by an order of magnitude or more compared with the defect-free alloy. The pores close to sample surface are the main fatigue crack initiation site, among which larger and deeper pore leads to a shorter fatigue life. The crack initiation is also affected by the pore geometry and direction. Besides, the overall porosity inside the bulk can affect the crack propagation during fatigue tests.

Preface to the special issue on aluminum alloys for transportation

Aluminum alloys have been used widely as structural materials in the field of aerospace,high speed train and car etc.due to their advantages such as low density,high strength,and good corrosion resistance.Improved properties of these materials can increase the reliability,durability and life of the structural components,and decrease the cost and CO_(2) emission.The special issue focuses on the recent development of advanced aluminum alloys applied in the transportation field,particularly aerospace,train and car.