Microstructural Characterization of a High-Strength Aluminum Alloy Subjected to High Strain-Rate Impact

The deformation and damage modes associated with the high strain-rate behavior of a high-strength aluminum alloy Al 2139 were analyzed. The microstructure was characterized at different physical scales to determine how the strengthening and toughening mechanisms of the alloy can inhibit and resist failure modes, such as shear localization and bending tensile failure, which occur due to high strain-rate impact. Grain morphology, precipitates (Ω and θ′), and Mn-bearing dispersed particles and inclusions were characterized by optical microscopy (OM), orientation imaging microscopy (OIM), energy dispersive spectroscopy (EDS), transmission electron microscopy/high-resolution transmission electron microscopy (TEM/HRTEM), selected area diffraction (SAD), and scanning electron microscopy (SEM) investigations of a 38-mm plate impacted by 4340 steel projectiles. Large grain sizes reduce grain boundary (GB) area and allow for more precipitation in the matrix, and these precipitates are shown to play a critical role in the toughening and strengthening of the alloy. Dispersed particles are associated with ductile failure, and inclusions are associated with ductile failure and shear failure. Different deformation modes were observed for the nanoscale precipitates, which affected overall behavior at size scales spanning the nano to the macro.     

Flow Behavior and Microstructural Evolution of 7A85 High-Strength Aluminum Alloy During Hot Deformation

Metallurgical and Materials Transactions A - Hot deformation behavior of 7A85 high-strength aluminum alloy was investigated at 593 K to 713 K (320 °C to...     

5182铝合金多道次热轧显微组织演变的实验模拟

结合美国Alumax铝业公司热轧工艺规程，在Gleeble 1500热模拟机上对5182铝合金多道次热轧过程进行了实验模拟，通过对各道次变形后显微组织的金相及显微硬度的测定，发现该合金与1050和3003铝合金相比在热轧过程中较容易发生再结晶，再结晶是一种主要的显微组织形态，其再结晶程度可用数学模型加以定量预测。     

7449高强韧铝合金均匀化热处理及微观组织演变

利用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱分析(EDS)、差示扫描量热(DSC)、X射线物相分析(XRD)研究了7449高纯高强韧铝合金均匀化热处理制度及其微观组织演变。结果表明:7449合金铸锭组织存在枝晶偏析,Zn,Cu原子沿晶界偏析严重,非平衡共晶相沿晶界呈连续网状分布,共晶相组成为α(Al)+Mg(AlZnCu)2四元相,初始回溶温度为477℃;合金经不同均匀化热处理后,非平衡共晶相发生回溶,且析出弥散分布的Al3Zr粒子。研究了不同的均匀化热处理制度对7449合金微观组织的影响,均匀化热处理温度越高,合金非平衡共晶相回溶效果越好,合金经(440℃/12 h)+(470℃/24 h)均匀化热处理后第二相回溶充分,且析出弥散的Al3Zr粒子,抑制后续加工和固溶处理过程中的再结晶。最终确定合金合理的均匀化热处理制度为(440℃/12 h)+(470℃/24 h)。     

Microstructural Inclusion Influence on Fatigue of a Cast A356 Aluminum Alloy

We examine the dependence of fatigue properties on the different size scale microstructural inclusions of a cast A356 aluminum alloy in order to quantify the structure-property relations. Scanning electron microscopy (SEM) analysis was performed on fatigue specimens that included three different dendrite cell sizes (DCSs). Where past studies have focused upon DCSs or pore size effects on fatigue life, this study includes other metrics such as nearest neighbor distance (NND) of inclusions, inclusion distance to the free surface, and inclusion type (porosity or oxides). The present study is necessary to separate the effects of numerous microstructural inclusions that have a confounding effect on the fatigue life. The results clearly showed that the maximum pore size (MPS), NND of gas pores, and DCS all can influence the fatigue life. These conclusions are presumed to be typical of other cast alloys with similar second-phase constituents and inclusions. As such, the inclusion-property relations of this work were employed in a microstructure-based fatigue model operating on the crack incubation and MSC with good results.     

均匀化工艺对2024高强度铝合金组织及性能的影响

通过采用金相显微镜、扫描电镜、力学拉伸试验机等检测手段,研究了2024高强度铝合金铸锭分别在均匀化温度480℃、495℃和510℃保温8h后经空冷和水冷方式处理后的组织及性能的影响.结果表明,经不同适合的均匀化工艺处理,铸态合金中的枝晶和非平衡低熔点共晶相逐渐溶解,晶界由连续分布逐渐转变呈不连续均匀分布状态.合金经49...     

高强铝合金的化学镀镍镀层性能研究

对高强铝合金进行了化学镀镍,观察了镀层形貌,对镀后试样进行了不同温度的热处理以及耐热性能试验,研究结果表明:经该工艺处理后镀层胞状形貌明显,结构致密均匀,孔隙少,镀层光亮,结合力好。400℃以下化学镀层的硬度随热处理温度的升高而增大,400℃处理后,镀层与基体的界面元素扩散现象明显。镀层在一定温度下具有保护铝基体的作用,尤其在瞬时高温的条件下镀层的保护作用更加明显。     

Experimental Investigation on Hydromechanical Deep Drawing of Aluminum Alloy with Heated Media

Temperature controlled sheet hydroforming is known as the innovative processing of warm/hot sheet hydroforming. Cylindrical cup hydromechanical deep drawing (HMD) at elevated temperature is the typical process for basic research. Warm HMD process was carried out on a warm sheet hydroforming experiment platform to investigate the influences of key processing parameters on formability. The process window of successful forming versus liquid pressure was obtained, which was manifested as a shape of pyramid. The region of successful forming in warm/hot sheet hydroming is a father set of that in cold sheet hydroforming. The microstructure evolution of cups formed by using warm HMD under the effect of temperature was investigated. The grain growth was observed compared with cold HMD. The hardness of hydroformed cup was tested and no apparent reduction of hardness was detected.     

Microstructural Characteristics and Mechanical Properties of Friction Stir Welded Thick 5083 Aluminum Alloy

Metallurgical and Materials Transactions A - Joining thick sections of aluminum alloys by friction stir welding (FSW) in a single pass needs to overcome many challenges before it comes to...     

Investigation of Microstructural Evolution in Ball-Milling of SiC Reinforced Aluminum Matrix Composites

Powder Metallurgy and Metal Ceramics - SiC reinforced Al–Mg–Si powders were ball-milled in a mixer device with different milling times. This process was performed to observe the...     

LC4铝合金晶粒的超细化处理研究

对LC4铝合金常规热轧板材进行了由470℃固溶处理2小时水淬+400℃8小时过时效+210℃压下量为90％的温轧+510或470℃1/2小时再结晶退火等工序组成的晶粒超细化处理,制得了平均晶粒直径小于7.0μm,厚1.5mm的薄板。上述晶粒超细化处理工艺参数中,过时效的温度和时间、温轧压下量和再结晶退火温度是通过四因素二水平的正交试验优选出的。取自该超细晶粒薄板的拉伸试样,在505℃和6.66×10~(-4)S~(-1)的初始应变速率条件下拉伸时,获得了0.5的m值和500％的延伸率,显示了良好的超塑性。     

Microstructural Aspects of Second Phases in As-cast and Homogenized 7055 Aluminum Alloy with Different Impurity Contents

The microstructural factors such as type, area fraction, morphology, distribution, and size of second phases in as-cast and homogenized 7055 aluminum alloy and the influence of impurity content variations have been investigated by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). In as-cast microstructures, the dominant second phases of η [Mg(Al, Cu, Zn)₂] with extended solubility of Cu and Al, a small amount of impurity phases of Al₇Cu₂Fe and Al₃Fe with a little solubility of Cu and Si, and trace Mg₂Si are identified. The variations of Fe and Si contents have no significant influence on the area fraction of η phases, but the area fraction of Fe-rich phase decreases from 0.231 to 0.102 pct with Fe content decreasing from 0.080 to 0.038 wt pct. Decreasing Fe contents reduces the size parameters of Fe-rich phases and refines their morphology correspondingly. After being homogenized at 753 K (480 °C) for 24 hours, η phases are largely dissolved, but the coarse impurity phases are insoluble. Compared with as-cast microstructures, the area fraction and composition of Fe-rich phases change a little but their morphologies are slightly coarsened.     

汽车用铝合金零件的半固态触变压铸工艺研究

针对半固态触变压铸工艺特点，对国产J1128卧式冷室普通液态压铸机的压射系统和模具系统进行了结构改进．对压铸工艺参数进行了优化选择，并采用半固态专用铝合金AlSi6Mg2和商用铝合金A357开展了大量半固态触变压铸试验研究。结果显示，半固态触变压铸工艺与普通液态压铸有很大的不同，在压射室和模具预热温度分别为100℃和250℃、低压压力为4．0MPa、射料二速工作压力为12MPa、增压压力为20MPa、快压射速度为1．4m／s的条件下，可获得充型完好的汽车用铝合金半固态压铸零件。     

Experimental Investigation on Square High-Strength Concrete Short Columns Confined with AFRP Sheets

An experimental investigation on square high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets is carried out in this study. Nine plain concrete specimens and 54 wrapped concrete specimens were tested under monotonic axial compressive loading. The specimens were grouped by three different grades of concrete strength. In each grade, some specimens were partially wrapped and others were fully wrapped, and the amount of wrapping AFRP sheets was varied also. Based on the experimental results, the regression formulas for strength and strain are obtained. The experimental results demonstrate that two types of axial stress-strain curves were observed depending on the form of AFRP wrapping, and the strength and ductility of the columns were increased when fully wrapped AFRP sheets, while only the strength was increased when partially wrapped AFRP sheets.     

试验测定和软件模拟绘制6063合金型材的TTT曲线

采用等温—电导率测试法和JMatPro 5．1软件模拟绘制了6063合金等温转变TTT曲线,研究了合金的淬火敏感性。结果表明,等温一电导率测试法得到的TTT曲线呈“C”型,淬火敏感区间为280～380℃。