挤压速度对搅拌摩擦反挤压法制备Cu-5%Ti_(2)SnC复合丝材性能的影响

对粉末冶金法制备的含5%(体积分数)Ti_(2)Sn CMAX相的初始复合材料进行搅拌摩擦反挤压(FSBE)处理,研究FSBE工艺的轴向横移速度对Cu-Ti_(2)Sn C复合线材显微组织、力学性能、电学性能和磨损性能的影响。结果表明,随着挤压速度的增加,显微组织中孪晶增多,Ti_(2)SnC颗粒细化,MAX相和Cu基体之间的界面结合改善。当转速为600r/min,轴向横移速度为25mm/min时,Cu-Ti_(2)SnC复合线材具有最大的硬度、屈服强度和极限抗拉强度,分别为HV 132.7、278.34MPa和485.15MPa,这是其更强的界面结合和更细的MAX相导致的。此外,当转速为600 r/min,轴向横移速度为25 mm/min时,Cu-Ti_(2)SnC复合丝的电导率最高,达到89.21%(IACS),磨损率最低,为0.0015 mg/m,这是其更大的晶粒尺寸、更强的界面结合与更低的密度导致的。

非等温时效对含银Al-Mg-Si合金多层摩擦表面显微组织和腐蚀行为的影响

研究非等温时效对添加不同银含量Al-Mg-Si合金多层摩擦表面显微组织和腐蚀行为的影响。通过在耗材棒横截面上钻孔的方式添加4%、8%和13%(质量分数)的银。采用光学显微镜和电子显微镜研究涂层的显微组织,采用显微硬度和拉伸实验研究涂层的力学性能,采用电化学测试研究样品的耐腐蚀性。结果表明,随着银添加量从4%(质量分数)增加到13%(质量分数),摩擦堆焊表面层的晶粒尺寸从(1.5±0.3)μm减小到(1.0±0.3)μm。铝基体中的溶质银能够加速Al-Mg-Si合金的析出动力学。经非等温时效处理后,含银涂层的屈服强度和抗拉强度分别比不含银涂层高50.6%和43.5%。经非等温时效处理后,材料的腐蚀电流密度降低,含银和不含银样品的耐腐蚀性均提高,含银涂层的耐蚀性比无银镀层提高了96.5%。

镍铝化物增强摩擦堆焊Al-Cu-Mg合金基复合涂层的非等温时效行为

本文研究了镍铝化物对Al-Cu-Mg合金非等温时效行为的影响。对经非等温时效处理的含镍铝化物Al-Cu-Mg合金的组织、力学性能和耐蚀性进行了评价。结果表明,在Al-Cu-Mg基体中加入1.5 wt%Ni后,Al-Cu-Mg基体中镍铝化物的存在使析出物由S-Al_(2)CuMg转变为θ-Al_(2)Cu。在非等温时效过程中,达到最大力学性能的非等温时效处理温度由250℃转变为300℃。与170℃等温人工时效处理相比,经非等温时效处理的含镍铝化物Al-Cu-Mg合金的最大硬度和力学性能均提高了9%。含镍铝化物试样在300℃时达到最大硬度和抗剪强度,分别为HV0.1(143.4±6.4)和(298.6±9.6)MPa。非等温时效处理后,与AA2024铝合金基体和不含镍铝化物涂层相比,含镍涂层的腐蚀电流强度分别降低了约58%和49%。与传统的人工时效处理相比,经非等温时效处理的含镍铝涂层的腐蚀电流降低了16.7%。

单辊驱动轧制对Al-5.6Zn-2.5Mg-1.4Cu铝合金显微组织、织构和力学性能各向异性的影响

研究在单辊驱动轧制Al-5.6Zn-2.5Mg-1.4Cu合金过程中,材料显微组织和织构的变化,并详细研究其力学性能各向异性与显微组织和织构的关系。对样品固溶处理后立即进行单辊驱动轧制,厚度减薄率分别为10%、20%、40%和60%。通过光学和扫描电子显微镜对显微组织进行表征,通过X射线衍射仪对织构进行表征,并对拉伸力学性能进行分析。结果表明,减薄率为40%和60%的轧制样品,其面内各向异性值从固溶处理合金的11.6%分别显著降低到2.4%和3.1%。这是由于旋转立方织构的形成减小了总的织构强度以及动态再结晶过程中新晶粒的形成。由于样品中晶粒形貌和织构不同,样品轧制方向(RD)比横向(TD)的屈服强度高。沿RD存在的几个较强取向导致沿RD(0°)的Portevin–LeChatelier(PLC)效应明显低于沿HD(45°)和TD(90°)的。随着厚度减薄率的增大,织构强度减小,导致RD、HD和TD之间的应变硬化率差异减小。而对于减薄率为60%的样品,其RD、HD和TD的断裂面无差异,说明其断裂行为为各向同性。

时效热处理对摩擦堆焊铝基复合材料显微组织和腐蚀行为的影响

研究人工时效热处理对Al−Zn−Mg−Cu基复合材料显微组织和腐蚀行为的影响。采用搅拌铸造工艺原位制备铝化镍增强Al−Zn−Mg−Cu合金复合材料,采用摩擦堆焊法将该铸态复合材料耗材杆堆焊在AA1050铝合金基体上,并在125℃进行人工时效热处理18 h。结果发现,无镍合金中晶粒发生明显长大。此外,复合材料显微组织中铝化镍增强相的存在导致双态组织的形成。富镍颗粒的存在和析出相的强化机制使含镍材料的硬度和强度得到提高。经人工时效热处理后,含铝化镍复合材料的剪切强度和硬度比铝基体分别提高了24%和13%。含镍颗粒的存在显著提高了未热处理合金的耐点蚀性能。经时效热处理后,含镍样品的耐腐蚀性比不含镍样品降低了39%,这是因为含镍样品中的富镍颗粒吸附了更多的可溶性铜。

AA1050表面Al-Mg-Cu_((p))复合涂层的力学和摩擦学性能

研究添加铜粉和改变耗材转速对AA1050铝合金基体上摩擦堆焊Al-Mg涂层力学和摩擦学性能的影响。铜粉是通过在耗材的横截面上钻孔的方式嵌入的。用光学显微镜和电子显微镜研究涂层的显微组织,用剪切实验研究涂层的力学性能。结果表明,当耗材转速从600 r/min增加到1000 r/min时,铜粉分布更加均匀,铜粉团聚现象减少,涂层的平均晶粒尺寸从(2.0±0.1)μm减小到(0.9±0.2)μm。随着转速的增加,富铜颗粒变小,并形成CuAl_(2)金属间化合物。当耗材转速从600 r/min增加到1000 r/min,使涂层从基体剥离所需的最大力从16.2 kN增加到18.4kN。转速为600、800和1000 r/min制备的涂层其磨损率分别比AA1050基材的低12%、18%和21%。

1050 铝合金基板上 Al−Mg−Si−Cu_((p))复合涂层的构建

利用摩擦堆焊工艺在AA1050铝合金基板上制备铜颗粒增强AA6061铝合金基复合材料涂层。研究耗材棒的增强相含量和预涂层热处理条件对涂层显微组织和力学性能的影响。结果表明,使用T6处理的耗材棒和增加铜含量使摩擦堆焊过程的温度升高。随着铜粉含量的增加,使用经T6处理和固溶态耗材棒制备的涂层的平均晶粒尺寸均减小,且与T6处理相比,用固溶态耗材棒制备的涂层的平均晶粒尺寸细16%。当铜的质量分数增加至20%时,使用T6处理耗材棒和固溶态耗材棒制备的涂层的耐磨性分别比AA1050基板提高了28%和24%。此外,使用T6处理和添加20%铜(质量分数)的耗材棒制备的涂层的剪切强度、硬度和耐磨性分别比使用固溶态耗材棒制备的涂层提高了4%、8%和5%。

Non-isothermal aging behavior of in-situ AA2024−Al_(3)NiCu composite

The effect of non-isothermal aging treatment on microstructure and mechanical properties of in-situ AA2024−Al_(3)NiCu composite fabricated by the stir casting process was examined.The Al_(3)NiCu intermetallic was created by adding 3 wt.%nickel powder during stir casting and homogenization treatment at 500℃ for 24 h after casting.The microstructural results obtained using optical and scanning electron microscope indicate that,after non-isothermal aging treatment,the S-Al_(2)CuMg precipitates become finer,forming a poor zone of this precipitate in the area between the dendrites.Also,adding nickel during stir casting reduces the precipitation rate and the contribution of S-Al_(2)CuMg precipitates in strengthening composite during non-isothermal aging.The maximum hardness,ultimate tensile strength,and toughness achieved in the 3 wt.%nickel-containing sample after non-isothermal aging at 250℃ are(121.30±4.21)HV,(221.67±8.31)MPa,and(1.67±0.08)MJ/m^(3),respectively.The maximum hardness and ultimate tensile strength of AA2024−Al_(3)NiCu composite are decreased by 6%and 4%,respectively,compared to those of nickel-free AA2024 aluminum alloy.

Theoretical and experimental studies on fabrication of two-layer aluminum−copper pipe by friction stir additive manufacturing

Using a friction stir additive manufacturing(FSAM)process,the fabrication of a two-layer aluminum−copper pipe was studied experimentally and numerically.For this purpose,by presenting a 3D thermo-mechanical model in ABAQUS software,the temperature and strain distributions during the process were studied.The simulation results show that,although the rotational-to-traverse speed ratio with a good approximation can predict the heat input during welding,it is not a precise measure to predict the occurrence of defects in the weld cross-section.There is a good agreement between the predicted and experimental thermal results,and the maximum relative error is 4.1%in estimating the maximum temperature during welding.Due to heat and severe plastic deformation in the stir zone,the aluminum−copper intermetallic compounds(CuAl_(2) and Cu_(9)Al_(4))are formed.The maximum hardness in the stir zone is 301.4 HV_(0.1) in sample welded with an overlap of−0.5 mm.The ultimate tensile strength and elongation of the two-layer pipe fabricated by friction stir additive manufacturing are(319.52±2.31)MPa and 19.47%,respectively.

Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

Microstructural characterization and mechanical properties of friction surfaced AA2024-Ag composites

The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.

Microstructure, mechanical and tribological properties of A390/SiC composite produced by compocasting

Aluminum A390 alloys reinforced with 10 wt.%SiC composite,were produced by the compocasting method.The effects of temperature,time,and stirring speed of this compocasting method on the microstructure,mechanical and tribological properties of composite were investigated.The results indicated that with increasing the rotational speed from 450 to 550 r/min,the distribution of the SiC particles becomes more uniform.A sudden increase in porosity due to gas absorption results in a downtrend of elongation with an increase in stirring speed from 550 to 650 r/min.Furthermore,as the stirring time increases,the amount of agglomerates of primary Si particles is reduced,and a more uniform microstructure of SiC and Si particles is formed.Although the fracture mode is a combination of both brittle and ductile fractures,the main mechanism of the fracture in the compocast sample is ductile.The formation of a protective layer at a high temperature can result in a very low wear rate as compared to a wear test performed at a low temperature.Optimal particle uniformity and mechanical properties were obtained at processing parameters of 610刟C,550 r/min,and 20 min.

Effect of reverse dual rotation process on properties of friction stir welding of AA7075 to AISI304

The friction stir lap welding of AISI304 stainless steel to AA7075 aluminium alloy was investigated using the conventional friction stir welding (C-FSW) and the reverse dual rotation friction stir welding (DR-FSW) processes. In order to reduce the heat input, a dual rotation tool with a lower shoulder rotating speed was used. The results showed that both processes provide welds with excellent appearance and free of internal defects. The use of the DR-FSW process with the tool shoulder rotating reversely at low speed results in larger grain refinement in the nugget and less change in the microstructure of the aluminium alloy than using the C-FSW. The use of DR-FSW process at low speed of rotation allows to reduce the amount of intermetallic compounds in the welding interface, but does not prevent their formation. Although DR-FSW welding exhibits tensile strength superior to that achieved with the conventional process (C-FSW), both exhibit brittle behaviour with fracture at the weld interface.

Influence of rotational speed in friction surfacing of nickel-aluminide reinforced aluminum matrix composite on commercially pure aluminum

The effect of rotational speed in the friction surfacing of nickel-aluminide reinforced Al-Zn-Mg-Cu alloy matrix composite on commercially pure aluminum was investigated. The nickel-aluminide reinforcement was fabricated by in-situ methods based on adding nickel powders to Al-Zn-Mg-Cu alloy melt during the semi-solid casting process.The findings showed that an increase in the rotational speed from 600 to 1000 r/min raised the coating efficiency from 65% to 76%. Besides, there was no significant difference between coating efficiencies in the coating with and without nickel-aluminide. The outcomes showed that if the coating was applied at a rotational speed of 1000 r/min, a traverse speed of 100 mm/min, and an axial feeding rate of 125 mm/min, the hardness and shear strength of the substrate increased by up to 225% and 195%, respectively. But the wear rate of the substrate dropped by 75%. Although the hardness of the coating containing nickel-aluminide increases by up to 32% compared to the coating without nickel-aluminide, nickel-aluminide does not affect the thermal stability of the coating.