Strength improving mechanism of laser arc hybrid welding of wrought AA 2219 aluminium alloy using AlMg5 wire

Abstract

Laser arc hybrid welding of wrought AA 2219 aluminium alloy was studied. The cross-weld tensile strength of the joint using AlMg₅ wire was 20% higher than that using AlCu₇ wire. The reasons for strength improvement were analysed by microstructure observations via scanning electron microscopy, transmission electron microscopy and electron backscattering patterns. The results showed the strength improvement of the joint using AlMg₅ wire depended on two reasons. One is the formation of large amount of fine S–Al₂CuMg precipitates. The other is the preformed pinning effect of the precipitates on the dislocations. Finally, the formation of the fine S–Al₂CuMg precipitates of the joint using AlMg₅ wire was discussed by thermodynamic calculation, and the formation of the preformed dislocation pining effect was discussed by the collision theory of adjacent dendrites during solidification.     

时效+再结晶退火对镍基合金锻造混晶组织的影响

为了消减镍基合金锻件中的混晶组织,本文提出了δ相时效+再结晶退火的热处理工艺路线。δ相在时效过程中可以直接析出或者由γ″相发生相变间接析出。对含析出δ相的材料进行高温再结晶退火,然后立即水冷,可以发现时效方式和时效时间对退火过程中的组织演变存在显著影响。时效过程中直接析出的δ相主要分布在晶界,随着时效时间延长部分晶粒内部也会析出δ相,其形貌以短棒状为主。间接析出的δ相主要分布在晶粒内部以及晶界,其形貌主要为晶内长针状以及晶界短棒状。短棒状δ相在退火过程中与位错交互作用较弱,主要起到钉扎晶界的作用;而长针状δ相能够促使亚晶的形成。因此,间接时效方式有利于再结晶形核的发生,并能够有效阻碍晶粒生长避免异常长大的再结晶晶粒。     

退火工艺对含钛超低碳搪瓷钢板成型和贮氢性能的影响

就罩式退火和连续退火工艺对含钛超低碳搪瓷钢板成型性能和贮氢性能的影响进行了研究。结果表明,试验材料经连续退火后其成型性能较罩式退火好;经罩式退火后钢中析出相的密度(单位体积内颗粒数)较连续退火的大,钢板氢穿透时间延长,氢扩散系数减小。试验材料经罩式退火后其贮氢性能优于连续退火。     

WC加入量对Ni60自熔合金喷焊层磨粒磨损性能影响

对Ｎｉ６０自熔合金中加入不同含量包ＷＣ粉末的喷焊层进行了磨粒磨损试验，结果表明，适量地加入ＷＣ可明显提高其抗磨粒磨损性能，观察了不同ＷＣ加入量对磨痕形貌的影响，初步探讨了ＷＣ的影响机制。     

Formation of carbonitride precipitates in hardfacing alloy with niobium addition

Niobium, as the most effective second-phase forming element, was added in the Fe-Cr13-C-N hard-facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The ther-modynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb(C, N) precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condition, a large number of secondary carbonitrides can pre-cipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and inter-granular chromium depletion.     

ZM81-xSn (x = 0, 2, 4, 6, 8 and 10)变形镁合金的组织演变和力学性能

通过对不同Sn含量的ZM81合金的微观组织和力学性能的测得,研究了Sn在ZM81合金中的存在形式和作用机制及不同添加量对合金显微组织和力学性能的影响。研究结果表明：Sn元素主要以Mg2Sn共晶相形式存在,能够细化铸态组织;热挤压过程中,Sn添加能够起到抑制动态再结晶和晶粒细化的作用;T6处理,尤其是双级时效,能显著提升挤压态合金的力学性能,其中ZM81-4Sn合金具有最佳的综合力学性能,抗拉强度、屈服强度和延伸率分别为416MPa、393MPa和4.1%。实验合金高强度主要源于MgZn2和Mg2Sn析出相的双重时效强化效果;相比单级时效,双级时效态合金的析出相细小弥散,因此其力学性能更优。     

Precipitates and hydrogen permeation in HSLA steel produced by TMCP

Abstract

The precipitates and hydrogen permeation behaviour were investigated in high strength low alloy steel produced by thermomechanical controlled processing with air/water cooling after finishing rolling, and the water cooled specimens were further tempered at various temperatures. Two types of precipitates have been found in the specimens. One is TiN with the size ranging from 50 to 300 nm, and the other one is fine NbC. The cooling and tempering treatment conditions affect the precipitation behaviour of NbC particles in α-Fe, leading to the difference in hydrogen permeation. The apparent hydrogen diffusivity in the air cooled specimen is lower than that in the specimen quenched and subsequently tempered at 300°C when the charging current density is 10 mA cm^?2. Increasing the tempering temperature to 500°C leads to the decrease of apparent hydrogen diffusivity; but the value is still higher than that in the air cooled specimen. However, the apparent hydrogen diffusivity slightly increases with further increasing tempering temperature from 500 to 650°C.     

铬含量对镍基合金涂层高温氧化行为的影响机理

采用增重法对铬质量分数分别为30%和40%～45%的两种镍基合金涂层在500℃、650℃和800℃下的高温氧化行为进行了研究.并使用配有能谱分析仪的扫描电镜以及X射线衍射仪等检测设备对涂层氧化产物的形貌、成分和相组成进行了分析.发现铬含量对镍基合金涂层的抗高温氧化性能和氧化机理有着重要的影响.铬含量为40%～45%的涂层,其表面生成了连续的Cr2O3保护膜,具有相对较低的氧化速度.     

超高W含量NiW中/重合金热加工行为研究

采用Gleeble-1500D研究了高密度Ni-42W-10Co-1Mo(wt.%)中/重合金(MHA)在1150~1300°C和应变速率0.001~1s_?1^{下流变行为和}微观组织演化规律。研究结果表明,该合金初始组织由面心立方基体和初生σ相构成。流变应力对变形温度和应变速率敏感,在1150℃变形,应力-应变曲线呈现出典型的动态回复软化特征,而在1200-1350℃变形呈现出典型动态再结晶软化特征。基于应力-应变曲线建立Arrhenius本构方程,计算得到Ni-42W-10Co-1Mo合金热变形激活能为446.2 kJ/mol。基于动态材料模型构建该合金热加工图,发现在1300℃高应变速率下存在失稳区。通过微观组织观察,揭示其动态再结晶机制主要为不连续动态再结晶,σ相促进动态再结晶优先在其周围形核。最终优化获得了Ni-42W-10Co-1Mo合金最佳的热加工窗口：1250–1300°C,应变速率0.1–0.01s_?1^。     

Fe、Al元素含量对Fe(2-x)CrMnAlxCu高熵合金组织性的影响

本研究将Fe、Al作为联合变量进行微调,检测并分析Fe、Al共同变化对Fe_(2-x)CrMnAl_xCu(x=1.3、1.4、1.5、1.6、1.7)高熵合金的相结构、微观组织、压缩性能、硬度、摩擦性能的影响。实验结果表明,Fe_(2-x)CrMnAl_xCu高熵合金的枝晶间及枝晶组织均由bcc相构成,且枝晶内部析出有序bcc相和FeAl相析出物,其析出物含量随着Fe含量减少,Al含量的增加略微增加,使得Fe_(2-x)CrMnAl_xCu高熵合金的硬度不断增加。当x=1.6时,高熵合金的综合性能达到最佳,其硬度高达558.5 HV,屈服强度为1205.43 MPa,抗压强度为1431.52 MPa,变形率为9.06%。并且在Fe含量减少,Al含量的增加的同时,高熵合金内的元素偏析的现象得到了一定程度的缓解。     

LF9镍基合金析出相的热力学模拟计算

采用Thermo-Calc热力学计算软件与相应的镍基高温合金数据库,计算了不同钛含量的4种LF9合金的可能析出的平衡相,研究了960、1 020℃两种固溶温度下钛含量变化对主要析出相的影响,分析了各相的析出规律.试验结果为进-步调整合金成分、改善合金力学性能提供了理论依据.     

镍基合金作粘结相的矿用硬质合金研究

采用Ni－Co－Cr－Mo等多元系合金作为硬质合金粘结相可以获得综合性能良好的矿用硬质合金材质,能够比较有成效地解决这一应用领域中钴代用问题。     

热处理温度对LaNi3.8Al1Mn0.2合金储氢性能的影响

对热处理(1173K, 1223K, 1273K, 1323K)前后LaNi3.8Al1.0Mn0.2合金的研究表明,热处理前后合金均由一个主相,三种第二相组成。热处理后第二相后变小,分布更加弥散,第二相中LaNi2变为LaNi相,晶胞参数和晶胞体积增加,活化性能变差,但吸放氢平台压降低,吸放氢平台的斜率和滞后变小,合金的吸氢速度显著变快,吸放氢焓变和吉布斯自由能的绝对值增大,而吸氢量未见明显变化。随着热处理温度的升高,晶胞参数和晶胞体积先增大后减小,吸放氢平台压先降低后升高,斜率先增大后减小,滞后先减小后增大,而焓变和自由能的绝对值先增加后减小,在1223K分别达到最大和最小值,而热处理温度的升高使活化性能和动力学性能略有提升。     

超超临界机组锅炉异种钢小径管镍基焊接接头超声波检测

针对超声检测火力发电厂锅炉小径管奥氏体钢与低合金钢对接异种钢焊缝的技术难题,文章通过理论分析、试验研究及现场检测验证,研究了常规小径管探头异种钢焊缝超声波检测方法。结果表明,对于如熔合线裂纹类缺陷选用小角度探头(K1～1.5)效果较佳;对于焊缝内缺陷宜选用大角度探头(K2～2.5)。利用该方法能有效检测出焊缝内各种缺陷,保证了机组安全运行也取得了较好的经济效益,对异种钢焊缝小径管超声波检测具有较强的借鉴意义。     

基于前向神经网络的镍基合金喷焊粉的硬度预测

利用前向神经网络,对镍基合金喷焊粉的硬度进行研究。通过对实验样本的学习训练,建立镍基合金粉的硬度值与其化学成分之间的隐性函数,用此神经网络,即可预测镍基合金粉材的硬度。     

He and Cr effects on radiation damage formation in ion-irradiated pure iron and Fe–5.40 wt.% Cr: A transmission electron microscopy study

The first walls of future fusion reactors will be exposed to 14 MeV neutron irradiation. In order to gain insight into their radiation resistance, model materials (a high purity iron and a Fe–5.40 wt.% Cr alloy) have been ion-irradiated in the JANNuS facility to high doses with and without helium. The materials were self-ion-irradiated at 500 °C up to ～100 displacements per atom (dpa) with gas implantation rates equal to 0, 2.5 and 25 appm He dpa^?1. He and Cr effects on the radiation damage formation have been studied at the microscopic scale by transmission electron microscopy. In pure Fe, a coarse dislocation network was observed after irradiation, irrespective of helium implantation rate. Concerning the V-containing features (nanobubbles or cavities), few large cavities were observed in pure iron irradiated without helium. The main effect of helium implantation was to increase their density and diminish their size. The main effect of chromium was to reduce the swelling for all the He implantation rates. Furthermore, in both materials, the cavity formation was mainly heterogeneous.     

Effects of grain size and precipitation on liquation cracking of AZ61 magnesium alloy laser welding joints

Abstract

Four kinds of wrought AZ61 alloy sheets with different microstructural features were successfully welded by CO₂ laser beam butt welding. Welding joints without visible pores were obtained under optimum process parameters. Effects of grain size and precipitation on liquation cracking behaviours of the laser welding joints were investigated. As far as the as rolled alloy sheets were concerned, liquation in the partially melted zone (PMZ) was visible along grain boundaries, and the extent of liquation was more serious in the alloy sheets with larger grains. As far as the as aged alloy sheets were concerned, plenty of precipitates (β-Mg₁₇Al₁₂) were involved and liquation in the PMZ was found both at grain boundaries and within grains. Moreover, the extent of liquation was more serious in the alloy sheets with more precipitates. It is promising to reduce liquation cracks in the PMZ of magnesium alloys by grain refinement, reducing the size and the quantity of the low melting point phase, and modifying its distribution.     

Phase change problem and effects of geometrical constants on weld pool geometry in sheet metal laser welding

Abstract

A three-dimensional quasi-state heat conduction model is presented for the solid/liquid interface in laser welding of thin sheet metals. The vapour plasma plume effect is incorporated into the model by considering the electromagnetic field equation to determine the laser power reaching the substrate surface after passing through the plume region. Optical properties, such as the dielectric constant and electrical conductivity of plume, and the thermal conductivity of the vapour of stainless steel 316 in the plume region are estimated. Elliptic-paraboloid weld pool geometry is considered and analytic expressions for temperature distributions are obtained in the solidand liquidregions based on theweld pool geometry. Experimental and theoretical results for the weld depths and widths areillustratedfor process parameters such as the laser power, welding speed, and weld pool shape factors in x and y directions.