Effect of Cu content on microstructures and mechanical properties of ADI treated by twostep austempering process

The effect of Cu content on the microstructures and mechanical properties(yield strength,ultimate tensile strength,impact energy,fracture toughness) of austempering ductile iron(ADI) treated by two-step austempering process were investigated. High Cu content in nodular cast irons leads to a significant volume fraction of retained austenite in the iron after austempering treatment,but the carbon content of austenite decreases with the increasing of Cu content. Moreover,austenitic stability reaches its maximum when the Cu content is 1.4% and then drops rapidly with further increase of Cu. The ultimate tensile strength and yield strength of the ADI firstly increases and then decreases with increasing the Cu content. The elongation keeps constant at 6.5% as the Cu content increases from 0.2% to 1.4%,and then increases rapidly to 10.0% with further increase Cu content to 2.0%. Impact toughness is enhanced with Cu increasing at first,and reaches a maximum 122.9 J at 1.4% Cu,then decreases with the further increase of Cu. The fracture toughness of ADI shows a constant increase with the increase of Cu content. The influencing mechanism of Cu on austempered ductile iron(ADI) can be classified into two aspects. On the one hand,Cu dissolves into the matrix and functions as solid solution strengthening. On the other hand,Cu reduces solubility of C in austenite and contributes more stable retained austenite.     

高温预处理及等温淬火工艺对CADI力学性能的影响

研究了高温预处理、奥氏体化温度(Tγ)及等温淬火温度(TA)对0.5%Cr含碳化物等温淬火球墨铸铁(CADI)的韧性、硬度的影响。结果表明,高温预处理可使CADI的冲击性能提高90%以上。当硬度为51.4~55.7 HRC时,冲击吸收能量(K)可达37.7~18.3 J。高温预处理后,随着Tγ的升高,CADI的K明显提高,硬度在一定范围内略有降低;随着TA的升高,CADI硬度逐渐降低,而K在260 ℃时达到最高。     

临界区回火温度对Fe-4Mn-1.2Cr-0.3Cu-0.6Ni中锰钢微观组织和力学性能的影响

研究了临界区回火温度对Fe-4Mn-1.2Cr-0.3Cu-0.6Ni中锰钢组织与力学性能的影响。通过热轧后直接淬火+临界区回火的工艺制备试验钢。采用光学显微镜(OM)、电子探针显微分析仪(EPMA)的扫描功能、透射电镜(TEM)、拉伸试验及冲击试验等对轧后淬火态和回火态试验钢的显微组织及力学性能进行了表征。结果表明,试验钢热轧后淬火可获得较高位错密度的板条马氏体,经过临界区回火后获得在回火马氏体基体上分布残留奥氏体的复合组织。随着临界区回火温度的升高,试验钢的抗拉强度呈升高趋势,而屈服强度先下降后增加,伸长率的变化趋势与试验钢中的残留奥氏体含量相关,冲击性能随临界区回火温度的升高呈先升高后降低的趋势。630 ℃回火后试验钢的拉伸性能最佳,650 ℃回火后试验钢的冲击性能最佳,确定最佳临界区回火温度区间为630~650 ℃。     

Effects of minor Ca on as-cast microstructures and mechanical properties of Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys

The effects of the addition of 0.6% Ca (mass fraction) on the as-cast microstructure and mechanical properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc magnesium alloys were investigated and compared by optical microscopy and scanning electron microscopy, differential scanning calorimetry analysis, and tensile and creep tests. The results indicate that the addition of 0.6% Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can refine the grains of the two alloys. At the same time, the addition of 0.6% Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can effectively improve the tensile properties of the two alloys. In addition, the addition of 0.6% Ca can also improve the creep properties of the Mg-3Ce-1.2Mn-0.9Sc alloy but is not beneficial to the creep properties of the Mg-4Y-1.2Mn-0.9Sc alloy. The different effects of minor Ca on the creep properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys are possibly related to the difference in the solid solubilities of Ce and Y in Mg.     

WSP流变铸造与球化处理对Al-18%Si-5%Fe合金组织和性能的影响

提出了波浪形倾斜板流变铸造(WSP)装置制备过共晶Al-Si-Fe合金的方法,对Al-18%Si-5%Fe合金流变铸造与球化处理进行研究。结果表明,WSP流变铸造可以明显改善合金中初晶硅、Al18Si10Fe5和Al8Si2Fe相的形貌。随着浇注温度降低,各相趋于细化和球化。WSP流变铸造过程中合金组织的形成源于3种机制:结晶雨带来的晶核增殖,斜板强冷却作用下晶体抑制生长和流动剪切作用下晶体破碎。WSP流变铸造与球化处理进一步改善Al-18%Si-5%Fe合金组织,合金维氏硬度达到87.5。在干摩擦条件下Al-18%Si-5%Fe合金的磨损率达到5.4 mg/h。     

表面机械研磨处理对316L不锈钢组织和性能的影响

对2.8mm厚的316L不锈钢板的上下表层进行机械研磨处理(SMAT),对经过不同时间的SMAT后的样品的表层组织进行金相观察,并测量SMAT不同时间的样品的硬度、抗拉强度.结果表明,经过表面机械研磨处理不同时间后,在316L不锈钢板表层获得了不同厚度的表面强化层,强化层组织为沿厚度方向由纳米晶层向微米晶层过渡的梯度组织;随着SMAT时间的增加,总的强化层厚度增加;表面组织的变化导致了表面硬度明显增加,整体材料的屈服强度增加;表面机械研磨处理时间对性能的影响并非线性增加,表面硬度和整体材料的屈服强度在处理5min时增加显著,处理时间继续增加到15、30和60min,它们的增加速度很小.拉伸断口表面形貌的扫描电镜观察表明,经过5min处理后的样品,表层的剪切唇变形区域面积增加,断口微观特征为长条状的韧窝,但是随着处理时间的增加,剪切唇区的尺寸并没有继续增加,而是开始下降,表面硬化区域的增加造成了塑性变形能力的下降.     

轴向压力对异种钢水下摩擦锥塞焊接头组织及力学性能的影响

在X52管线钢上采用Q345塞棒进行水下摩擦锥塞焊工艺试验研究,讨论轴向压力对塞焊接头组织和力学性能的影响. 结果表明,对给定7 000 r/min焊接转速在30 kN轴向压力下,塞焊缝底部圆角过渡处易产生未结合缺陷,随着轴向压力增加达到35 kN以上,可以获得完全结合的致密塞焊缝,焊缝顶锻区及底部圆角过渡处的热影响区也不断扩大. 由于水介质快速冷却作用,焊缝区组织特征比较复杂,主要由板条状马氏体和板条状贝氏体组成,硬度分布不均匀并产生明显淬硬现象其硬度可达450 HV1. 在0 ℃下焊缝中心冲击吸收能量也会随着轴向压力的增加而不断提高,最高可以达到62 J,但远低于母材的267 J.     

Al-Ti-C-Sr对A356合金组织和性能的影响

在A356熔体中分别加入自制的Al-5Ti-0.25C-2Sr和Al-5Ti-0.25C-8Sr中间合金,研究了这两种中间合金对A356合金显微组织和力学性能的影响.结果表明,向A356中分别添加质量分数0.5%的Al-5Ti-0.25C-2Sr和Al-5Ti-0.25C-8Sr后,A356合金晶粒尺寸由42.5 μm分别减小至33.2 μm和30.6 μm,共晶硅从粗大的针片状转变为细小的短杆状或点状;T5处理后,添加Al-5Ti-0.25C-8Sr的A356合金的共晶硅粒状化效果较未添加Al-Ti-C-Sr的和添加Al-5Ti-0.25C-2Sr的好一些,其共晶硅颗粒均匀细小,圆整度高;加入质量分数0.5%的Al-5Ti-0.25C-2Sr或Al-5Ti-0.25C-8Sr后,T5态A356合金的抗拉强度由217.6 N/mm2分别提高到235.8 N/mm2和248.2 N/mm2,伸长率由10.1%分别提高到11.2%和11.8%.     

Effect of vibration on microstructures and mechanical properties of 304 stainless steel GTA welds

This study investigates the microstructures and mechanical properties of 304 stainless steel at various vibration frequencies during simultaneous vibration welding. The experimental results demonstrated that simultaneous vibration welding could accelerate the nucleation and grain refinement of the microstructures. The effect of the grain refinement was more evident at the resonant frequency (375 Hz) and a minimum content of residual δ-ferrite (4.0%). The γ phase grew in the preferential orientation of the (111) direction with and without vibration. The full width at half maximum of the diffraction peak widened after the vibration, which was attributed to the grain refinement. The residual stress could be efficiently removed through simultaneous vibration welding when the amplitude of the vibration was increased. Furthermore, the lowest residual stress (139 MPa) was found when the vibration frequency was 375 Hz. The hardness and Young’s modulus exhibited slight increases with low and medium frequencies. The hardness values were increased by 7.6% and Young’s modulus was increased by 15% when the vibration frequency was resonant (375 Hz).     

预共晶条件下单晶硅接头的组织性能研究

通过在单晶硅表面预制一层Au-Si熔敷层,利用Au -Si低温共晶原理实现预共晶条件下单晶硅的低温扩散连接.分析表明,在界面的共晶组织中,Si的生长形态受晶体学取向和生长环境共同作用.由于Au-Si互不相溶,随着温度的升高,晶粒呈枝蔓状生长,其中某些晶粒沿着基体生长并最终实现基体的桥状连接.分析认为,随着预共晶温度的升...     

铁素体区轧制对超低碳钢和无间隙原子钢组织和力学性能的影响

本文研究了铁素体区轧制工艺条件对超低碳(ULC)钢和钛处理的无间隙原子(Ti-IF)钢组织和性能,特别是对深冲性能的影响,并分析了Ti-IF钢中的析出物.结果表明,润滑条件对Ti-IF钢的塑性应变比(r)值和深冲性能影响显著,但对ULC钢的r值影响很小.随铁素体区轧制温度的降低,Ti-IF钢的深冲性能得到提高,但ULC钢即使在铁素体区低温轧制其r值仍小于1,深冲性能较差.     

Effects of microstructures on mechanical properties of Ti-63 titanium alloy

The microstructure and mechanical properties of Ti-63 pancakes were investigated under different heat-treatment modes. Pancake No. 1, with an as-forged bimodal structure, was β annealed at 930°C for 1 h. Its structure was changed to a Widmanstatten structure with continuous grain boundary α phase and long lamellar α phase. The pancake showed a good combination of strength, ductility and fracture toughness. Pancake No. 2, with an as-forged bimodal structure, was aged at 540°C for 8 h after annealing at 930°C for 1 h. Other than the fine secondary α precipitates, it showed a similar microstructure to that of pancake No. 1. The fine precipitates can enhance the pancake’s strength while reducing the ductility and fracture toughness. Pancake No. 3, with an as-forged basket-weave structure, was annealed at 750°C for 1 h. Its structure was nearly unchanged and it achieved a better ductility but a slightly lower fracture toughness than pancake No. 1.     

终轧温度和冷却工艺对铁素体贝氏体双相钢组织和力学性能的影响

利用Gleeble-2000D热模拟机、550 mm轧机、扫描电镜等研究了终轧温度和冷却工艺对铁素体贝氏体双相钢组织和性能的影响。首先,在水冷-空冷-水冷模式下研究终轧温度对显微组织和力学性能影响,结果表明:随终轧温度降低,基体组织带状加剧,且铁素体形态由多边形转变为沿轧制方向变形的椭圆形;当终轧温度低于800℃时,铁素体比例明显增加,贝氏体比例下降,抗拉强度下降。其次,在850℃的终轧温度下研究了冷却工艺对显微组织和力学性能的影响,结果表明:当终轧后冷却方式为水冷时,基体组织以准多边形铁素体和针状铁素体为主,伸长率较低;终轧后采用水冷-空冷-水冷方式冷却时,基体组织以块状铁素体和贝氏体为主,伸长率较高。     

Effects of Sc and Mn on microstructures and mechanical properties of Mg-Gd alloy

Two alloys of Mg-12.4Gd and Mg-12.5Gd-0.8Sc-1.4Mn were prepared. Hot extrusion and T5 heat treatment were conducted, and then the mechanical properties of the two alloys were tested at room and high temperatures. The effects of Sc, Mn on the microstructures of Mg-12.4Gd were investigated by optical microscopy, scanning electron microscopy and transmission electron microscopy. The results demonstrate that after hot-extrusion the alloying with Sc, Mn can efficaciously refine the grains of Mg-12.4Gd alloy; and increase the elongation at room and high temperatures after T5 heat treatment. But the strength at high temperature is not obviously improved.     

Effects of Y content on microstructures and mechanical properties of as-cast Mg-Zn-Nd alloys

The effects of Y addition amount on the microstructures and mechanical properties of as-cast MgZn-Nd alloy have been investigated by using an optical microscope, a scanning electron microscope, backscattered electronic imaging technique, an X-ray diffractometer, a differential thermal analyzer and a universal testing machine. There are three kinds of ternary phases in the Mg-Zn-Y system alloys, such as I phase(Mg3Zn6Y), W phase(Mg3Zn3Y2) and Z or X phase(Mg12Zn Y). The experimental results in the present study indicate that the Mg-Zn-RE(RE includes Y and Nd) ternary phases change from the I + W phases in turn to unique W, W + Z and unique Z as the Y content increases from 0% to 3%. Simultaneously, their distribution gradually changes from small particle-like form to continuous network form. The grain size first decreases as the Y content increases from 0% to 1% Y, then increases when the Y content exceeds 1% and finally decreases again when the content exceeds 3% due to the variation of growth restriction factor caused by the increased Y element and the change of the ternary phases. The hardness continuously increases because of the increased ternary phase amount. The ultimate tensile strength and elongation first increase within the range of 0-1% Y, also due to the increased ternary phase amount and grain refinement, and then decreases because of the grain coarsening, porosity formation and continuous network distribution of the ternary phases. The grain bonding strength of the W phase-containing alloys is quite strong and the W phase is an ideal strengthening phase if a given amount of it distributes in discontinuous and small-sized form. The alloy with 1% Y only has one ternary phase of W, but has the best combination of mechanical properties. The fracture regimes of these alloys always present a transgranular mode.     

Effects of rheoforming on microstructures and mechanical properties of 7075 wrought aluminum alloy

It is economically advantageous to cast wrought aluminum alloys directly into near-net-shape components.The objective of the present work is to take advantage of the rheoforming with 7075 alloy to improve the competitiveness of this emerging technology in the manufacture of wrought aluminum alloy.High quality semi-solid slurry was produced,in which primary α(Al) presents in diameter of 62 μm and shape factor of 0.78 and features no eutectics entrapped.Higher forming pressure results in small grain size,improved shape factor and higher density.Especially,rheoforming can effectively reduce the occurrence of hot tearing.The average yield strength and elongation of the rheoformed samples in the T6 condition are 483 MPa and 8%,respectively.     

Effects of ZrC and SiC addition on the microstructures and mechanical properties of binderless WC

ZrC-added WC ceramics and SiC-added WC–2 mol% ZrC ceramics were sintered at 1800 °C using a resistance-heated hot-pressing machine. Dense WC ceramics containing 0–1 mol% ZrC and WC–2 mol% ZrC ceramics containing 1–6 mol% SiC were obtained. The reaction products W₂C, ZrO₂ and ZrC-based solid solutions were formed in the ZrC-added WC ceramics during sintering. The relative amount of W₂C reached zero at 2 mol% ZrC, increased in the range of 2–6 mol% ZrC, and decreased again above 6 mol% ZrC. The average WC grain size decreased from 0.49 μm for the WC ceramic to 0.24 μm at 4 mol% ZrC. The SiC addition of 1–2 mol% to the WC–2 mol% ZrC ceramics caused abnormal growth of WC grains. The Vickers hardness of the ZrC-added WC ceramics decreased to 17 GPa at 2 mol% ZrC. The hardness of the SiC-added WC–2 mol% ZrC ceramics increased from 12.4 at 2 mol% SiC to 21.5 GPa at 6 mol% SiC. The fracture toughness of the ZrC-added WC ceramics decreased from 6.2 MPa m^0.5 for the WC ceramic to 5.2 MPa m^0.5 at 4 mol% added ZrC. The fracture toughness of the WC–2 mol% ZrC ceramics with 6 mol% SiC were relatively high at 6.7 MPa m^0.5. The addition of SiC to WC-based ceramics thus improved both hardness and fracture toughness.     

固溶处理对Fe-Mn-Al-C系低密度钢组织与性能的影响

采用OM、SEM、TEM、XRD等试验方法,对不同固溶温度下Fe-27Mn-8Al-1.6C低密度钢的力学性能和组织演变规律进行了研究。结果表明,Fe-27Mn-8Al-1.6C钢的密度为6.8 g/cm³。固溶处理对该钢的组织与性能影响较大,高温固溶后试验钢奥氏体晶界间有少量к-碳化物,随着固溶温度的升高,晶界间未溶к-碳化物含量减少直至消失,奥氏体中C含量逐渐增加;在1000 ℃固溶处理后,试验钢具有最佳的强塑性配合,抗拉强度为1266 MPa,断后伸长率为34%,强塑积可达43.1 GPa·%;在冷却过程中,试验钢基体发生调幅分解,大量细小的к-碳化物弥散分布在奥氏体内。     

Effects of Ce and Ti on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy

1. Introduction Heat-treated aluminum alloys are required for several structural applications. Several efforts have been made to improve the mechanical properties of the alloys that are currently in use and also to de-velop a novel series of alloys. The approaches used are: alloy modification, or processing modification, or both. The strength of aging-hardenable alloys such as Al–Cu–Mg series relies upon the strength-ening precipitates that are formed during aging after quenching. The agin…