选区激光熔化成形AlSiMg3合金

基于选区激光熔化（SLM）技术熔体快速冷却的特点，通过提高Al-Si-Mg合金中Mg的含量，设计获得SLM技术专用AlSiMg3合金。系统研究了不同工艺参数和时效处理条件对SLM成形AlSiMg3合金组织和硬度的影响。结果表明，SLM成形样品均由α-Al、Si和Mg2Si相构成。高激光能量密度有利于增加粉末样品的成形性，当激光功率为160 W，扫描速度为200 mm/s时，样品具有最低孔隙率0.07%。随着激光扫描速度的增加，样品中富Si组织的比例逐渐升高，Mg元素在α-Al中固溶量逐渐增大，使得SLM成形样品的硬度逐渐升高，最大值为194±3 HV。样品经150 ℃时效处理后，由于α-Al内部纳米颗粒的析出，导致样品硬度增大，最大值为210±2 HV，远高于现有报道的SLM成形Al-Si和Al-Si-Mg铝合金。本研究报道了成形性和力学性能优异的SLM专用Al-Si-Mg合金。     

Effects of welding parameters and welding sequence on residual stress and distortion in Al6061-T6 aluminum alloy for T-shaped welded joint

The distribution of temperature and then the distribution of residual stress and distortion in the stiffened aluminum alloy Al6061-T6 plates under the metal inert gas (MIG) welding process were investigated by three dimensional thermo-mechanical coupled finite element model using Ansys software. The properties of materials were considered temperature-dependent and the filler metal was added to the workpiece by the element birth and death technique. In three modes of current, two different speeds and two various sequences, the distribution of residual stress and distortion were calculated and analyzed. The results showed that increase in welding speed decreased the vertical deflection in the plate, transverse shrinkage and angular distortion of plate and the lateral deflection of stiffener, but increased the maximum longitudinal tensile stress in the plate and stiffener. Furthermore, increase in current increased the residual stress and deformation in the plate and stiffener, and the change in the welding sequence changed the distribution of the distortion in the plate and the stiffener without significant change in the distribution of the longitudinal residual stress.     

Influence of heat treatment on corrosion behaviors of 316L stainless steel in simulated cathodic environment of proton exchange membrane fuel cell (PEMFC)

The influences of two types of heat-treatments on the corrosion behavior of 316L SS in the simulated cathodic environment of PEMFC, are investigated using potentiodynamic curve, electrochemical impedance spectroscopy (EIS), Mott-Schottky plot and auger electron spectroscopy (AES), respectively. The results show that 316L SS is in the passive state within the potential region from −0.1V_SCE to 0.8V_SCE in the simulated cathodic environment of PEMFC, and a passive film can be formed on 316L SS. The passivity of 316L SS in the simulated cathodic environment of PEMFC firstly increases and then degrades with the increased solid solution temperature or time, and the best passivity corresponds to the solid solution temperature at 1050 °C for 40 min among other solid solution treatments. While 316L SS heat-treated with the solid solution treatment at 1050 °C for 40 min plus aging treatment at 900 °C for 4 h, also has the best passivity in the same solution among other solid solution plus aging treatments. The best corrosion protection, lowest donor density and the highest thickness of the passive film corresponding to the solid solution temperature at 1050 °C for 40 min among other solid solution or solid solution plus aging heat treatments, and this treatment is mostly suitable for improving the anti-corrosion property of 316L SS in the simulated cathodic environment of proton exchange membrane fuel cell (PEMFC).     

Corrosion behaviour of an industrial shot-peened and coated automotive spring steel AISI 9254

A high-strength low-alloy steel, AISI 9254 (54SiCr6), is widely used for suspension spring production in the automotive industry. In this work, industrially manufactured zinc phosphate coated helical springs are subjected to detailed microstructural and surface analysis for better understanding of corrosion evolution. The material’s free corrosion potential and anodic/cathodic behaviour were investigated in NaCl solutions and corrosion propagation mechanisms were studied using potentiostatic polarisation on cross-sectional and external surfaces. The bulk material is fully martensite with uniformly distributed MnS inclusions, while the spring surface has a 2–3?μm mechanically deformed region introduced by shot-peening and a thin zinc phosphate coating. The corrosion open circuit potential of bulk material and shot-peened spring surface was about –0.7V_SCE without significant difference, while phosphated surface is more noble (more positive potential). MnS inclusions, stimulating the anodic attack in the steel, influence corrosion propagation and pit morphology to a large extent that can have an impact on the spring performance.     

自然时效效应及预时效处理对7A20铝合金组织性能的影响

研究了中强度7A20铝合金的自然时效硬化效应及预时效处理对组织和性能的影响。采用光学显微镜和透射电镜表征了其微观组织结构,采用维氏硬度计和万能拉伸试验机测试了其硬度和力学性能。结果表明:固溶态7A20试验铝合金的自然时效硬化效应明显,12天后硬度由56 HV0.5提高到122 HV0.5,提高了117.86%。经120 ℃×10 min预时效处理后,自然时效硬化增量最低,相比于固溶态降低了16 HV0.5,有效抑制自然时效硬化效应;同时,预时效处理提升了烘烤硬化效应,烘烤硬化后屈服强度提升了166 MPa,抗拉强度提高了51 MPa,伸长率降低了7%。烘烤处理前,其晶内的强化主要来自于与基体共格的GP区,烘烤处理后为尺寸小于5 nm、弥散分布的η′强化相。     

Nb和时效时间对热轧中锰TRIP钢中P偏聚的影响

热轧态中锰TRIP钢首先经650 ℃退火2 h,随后在550 ℃进行等温时效热处理,采用场发射扫描电镜(FE-SEM)研究该钢中P的偏聚和时效析出行为的变化情况。结果表明,中锰TRIP钢中P在晶界的偏聚是一种非平衡偏聚现象,临界时间约为50 h,与理论计算结果48 h较为吻合。在局部偏聚区域内,C与P存在共偏聚的关系,即P偏聚量高的地方,C含量也高。而合金元素Nb具有抑制P偏聚的效果,在20~70 h时效时间内,可以相对降低6.57%~19.5%的最大P偏聚量。根据电子背散射衍射(EBSD)菊池线分析,P偏聚量低于2.28at%时,P为固溶状态,高于2.28at.%时,P为析出状态。     

采用轮廓特征匹配的红外-可见光视频自动配准

为了精确地配准近平面场景下的红外-可见光视频序列,本文提出了一种基于轮廓特征匹配的自动配准方法,通过迭代匹配目标轮廓特征来解决异源图像中配准特征的提取和匹配难题。首先,采用运动目标检测技术获取目标轮廓,并由曲率尺度空间(CSS)角点检测算法提取轮廓特征点。此后,建立全局形状上下文描述子和局部边缘方向直方图描述子描述特征,从而实现可靠的特征匹配。来自不同时刻的匹配点对被保存在一个基于高斯距离准则的特征匹配库中。最后,为了克服近平面场景中目标深度变化的影响,本文结合前景样本随机抽样策略计算配准矩阵的损失函数,完成对全局配准矩阵的更新。在LITIV数据库上对方法进行实验验证,结果表明本文方法的配准精度优于当前先进的对比方法,在9个测试视频上的平均重叠率误差仅为0.194,与对比方法相比下降了18.5%。基本满足了近平面场景下红外-可见光视频序列配准的精度要求,且具有较高的鲁棒性。     

港里矿软破围岩采矿的分析与研究

港里矿围岩软弱破碎，随开采深度延伸，地压显现越来越剧烈，严重影响港里矿正常回采。为研究港里矿软破围岩采矿，分析了影响采矿正常进行的因素和机理，调整采矿的顺序，使港里矿软破围岩采矿的困难得到根本扭转，保证了采矿生产的正常进行，选择围岩稳固及充分卸压部位布置斜坡道和联巷、优先回采围岩破碎的高应力区是地压管理的关键问题。