半固态粉末医用Mg-6Zn合金表面涂层改性设计

为提高医用镁合金的耐腐蚀性,本文对镁合金进行表面改性处理。通过在电解液中添加纳米铜粉和醋酸铜两种形式不同浓度铜离子,采用微弧氧化在最优参数(电流密度6A/dm2,氧化时间20min)下Mg-6Zn合金基材表面涂层,分析不同添加形式和浓度下复合涂层的形貌、元素分布、物相、腐蚀性能、显微硬度等影响规律。结果表明,在相同浓度的情况下,纳米铜电解液所得涂层的粗糙度是高于醋酸铜电解液得涂层的粗糙度。通过电化学实验发现醋酸铜涂层中30%涂层样品耐蚀性最好,纳米铜粉涂层中25%涂层样品的耐腐蚀好。同浓度的样品,纳米铜粉涂层的腐蚀速率是大于醋酸铜涂层的腐蚀速率,说明纳米铜粉涂层的耐腐蚀性是强于醋酸铜涂层的。

温度与保温时间对半固态粉末轧制AA2024带材性能与显微组织的影响

采用半固态粉末轧制法制备2024铝合金带材,研究粉末加热温度和保温时间对轧制力、带材的相对密度及显微组织的影响。结果表明:2024铝合金带材的相对密度随粉末温度升高而增大,随保温时间延长而提高。粉末在585℃保温40 min后轧制,可获得形貌规整、无表观缺陷且晶粒细小均匀的等轴晶带材,带材相对密度达到93.28%。半固态粉末轧制力仅为室温下固态粉末轧制力的33.5%。半固态粉末轧制带材组织内仍存在少量孔隙,进一步热轧后可达到近全致密,显微硬度提高77.8%。因此,半固态粉末轧制对于缩短工艺流程,减小轧制力,制备高致密度的2024铝合金带材具有明显的优势。

半固态粉末轧制法制备SiC_p/AA2024复合带材的显微组织与力学性能

以组合雾化法制备的2024铝合金粉末和SiC颗粒为原材料,采用半固态粉末轧制法,在575~635℃温度下制备10%SiC_p/AA2024复合带材,研究粉末加热温度对带材显微组织与力学性能的影响,并与相同条件下制备的AA2024铝合金带材进行对比。结果表明:升高粉末加热温度可促进AA2024粉末变形或破碎,所得10%SiC_p/AA2024复合带材具有半固态特征的球状或近球状显微组织。与AA2024合金带材相比,SiC_p/AA2024复合带材的基体晶粒更加细小。SiC颗粒与液相Al没有发生显著的界面反应,未生成对体系有害的Al4C3物质。SiC_p/AA2024复合带材和AA2024合金带材的屈服强度、抗拉强度及伸长率都随粉末加热温度适当升高而提高,SiC_p/AA2024带材的屈服强度和抗拉强度分别在366~412 MPa和425~514 MPa之间,均明显高于AA2024合金带材,伸长率为3.1%~4.9%,断裂方式主要为脆性断裂。AA2024带材的屈服强度在265~348 MPa范围内,抗拉强度为362~423 MPa,拉伸断裂方式随加热温度升高由脆性断裂向韧性断裂转变。

半固态粉末成形温度对Mg-6Zn-xMn显微组织和力学性能的影响

使用金属镁、锌、锰粉为原料,采用半固态粉末成形法在540~600℃下制备Mg-6Zn-x Mn(x=0.5%和1.0%,质量分数)合金,通过光学显微镜、X射线衍射仪、扫描电镜、显微硬度仪、万能试验机、电化学测试等表征和测试手段,研究成形温度对合金物相和晶粒大小、抗压强度和显微硬度,以及耐腐蚀性能的影响。结果表明,随成形温度升高,合金的相对密度和平均晶粒尺寸增加,但显微硬度和抗压强度降低。成形温度从540℃升高至600℃,Mg-6Zn-0.5Mn和Mg-6Zn-1.0Mn合金的抗压强度从382.8MPa和372.1MPa下降至348.9MPa和353.1MPa(分别下降约8.9%和5.4%),主要是由于成形温度升高,晶界处生成更多的氧化物夹杂,从而使合金的抗压强度降低。合金的显微硬度(HV)均在95.1以上,600℃成形的Mg-6Zn-0.5/1.0Mn合金具有最好的耐腐蚀性能,电化学腐蚀速率分别为0.263 mm/a和0.183 mm/a。

半固态粉末成形医用Mg-6Zn合金的预压过程数值模拟

将Mg-6Zn混合粉末看作可压缩连续介质,运用MSC.Marc软件对半固态粉末成形医用Mg-6Zn合金的预压过程进行数值模拟,为工艺优化提供理论指导。通过模拟预压过程中的相对密度、压制力和脱模力的变化,并与实验结果进行验证。结果表明,不同的保压时间、压制速度和摩擦系数对相对密度分布均有影响,但摩擦系数对相对密度分布的影响最为突出;通过对比优化前后等效应力的分布情况,发现优化工艺参数后应力集中现象得以缓解。由此可见,该模型具有良好的可靠性。

半固态粉末压缩Mg-6Zn合金过程数值模拟

基于半固态热模拟压缩实验推导出的粉体材料本构方程,运用MSC.Marc软件对半固态粉末成形医用Mg-6Zn合金的压缩过程进行了数值模拟,分析了致密化过程中相对密度、粉末位移变化情况,并对模型的可靠性进行了实验验证,探究了温度对半固态粉末成形的影响规律。结果表明:液相分数低于10%时,成形温度对相对密度的影响不大,且随着压缩的进行,相对密度逐渐增加并趋于稳定;半固态粉末成形应力集中在圆柱压坯边缘两端处,应力最小值出现在圆柱坯的中心两端和边缘处“鼓肚”区;该模型在低液相分数下具有良好的可靠性,而液相分数较高时误差很大,液相是产生误差的根本原因。

Al-Cu-Mg合金粉末在半固态的组织演变及晶粒粗化机制

将Al-Cu-Mg合金粉末及其粉末烧结体分别加热到833 K、843 K、853 K、863 K、873 K、883 K和893 K,并保温60 min、50 min、40 min、30 min、20 min、10 min和0 min后水冷得到其半固态微观组织。通过计算半固态粉末及其烧结体的晶粒尺寸、形状因子和晶粒粗化速率,分析其组织演变规律,同时对比分析了相同成分下粉末与致密材料在半固态下的晶粒粗化机理。结果表明:随着半固态温度的提高和保温时间的延长,粉末的晶粒尺寸增加;为避免获得粗大晶粒,Al-Cu-Mg合金半固态粉末成形的参考温度应低于883 K,保温时间应在40 min以内;随着温度的提高,粉末的晶粒粗化速率增大,在883 K时达到19μm^(3)/s,但远远小于同成分下致密材料的粗化速率,这是半固态粉末成形技术能够获得细小组织的一个重要原因。

Microstructural evolution of gas atomized Al-Zn-Mg-Cu-Zr powders during semi-solid rolling process

Under H2 atmosphere, the green strips were prepared from Al-5.8Zn-1.63Mg-2.22Cu-0.12Zr(mass fraction, %) powders by the semi-solid rolling process with a relative density from 76.1% to 88.0%. The role of temperature on microstructure and mechanical properties was investigated. With increasing rolling temperature from 580 to 610 °C, the disappearance of primary powder boundary and isolated pores, inter-diffusion of species and the change of grain boundary were accelerated. Moreover, the mechanism of microstructure evolution changes from the densification dominant regime to the coarsening dominant regime; the amount of η(MgZn2) phase decreased and more Al2 Cu particles precipitated at grain boundaries. The optimum temperature for semi-solid rolling of Al-5.8Zn-1.63Mg-2.22Cu-0.12 Zr powders was determined. The liquid fraction in the range of 53% to 67% corresponds with a high density level of green strips. The present experimental analysis suggests that semi-solid powder rolling can be optimized to manufacture strips with high mechanical properties.

粉末轧制成形技术研究进展

介绍了粉末轧制过程,论述了粉末轧制技术的工艺参数、技术改进和以其为基础开发的半固态粉末轧制技术,阐述了近些年来粉末轧制技术的应用情况,最后对这些技术进行了总结和展望。

Effects of processing parameters on microstructure and mechanical properties of powder-thixoforged 6061 aluminum alloy

A new processing technology,powder thixoforming,for preparation of particle reinforced metal matrix composites was proposed and 6061 aluminum alloy was prepared by powder thixoforging.6061 ingots were first prepared by cold-pressing the atomized 6061 alloy powders,and then the ingots were partially remelted followed by thixoforging.The effects of reheating time,mould temperature and reheating temperature on microstructure and mechanical properties of the thixoforged alloys were investigated.The results indicate that all of the three parameters have large effects on the microstructure and mechanical properties.Owing to the microstructure changes,the fracture regime varies with the processing parameters.Furthermore,cracks always initiate from shrinkage porosities and inclusions,and then propagate either along the secondarily solidified structures or primary particles.The ultimate tensile strength,elongation and hardness of the resulting alloy are up to 196 MPa,11.0%and HV 55.7 respectively.

Densification process of 10%B_4C-AA2024 matrix composite strips by semi-solid powder rolling

Semi-solid powder rolling（SSPR） is a novel strip manufacturing process,which includes the features of semi-solid rolling and powder rolling.In this work,densification process and deformation mechanisms of B4 C and AA2024 mixed powders in the presence of liquid phase were investigated.The relationships between relative densities and rolling forces were analyzed as well.The results show that liquid fraction plays an important role in the densification process which can be divided into three stages.Rolling deformation is the main densification mechanism in deformation area when the liquid fraction is lower than 20%.When the liquid fraction is equal to or higher than 20%,the flowing and filling of liquid phase are the densification mechanisms in deformation area.The relative densities increase with increasing rolling forces.The relative density–rolling force curves are similar at 550 °C and 585 °C.The characteristics of the curve shapes are apparently different at 605 °C and 625 °C.

Microstructural and mechanical behavior of blended powder semisolid formed Al7075/B_4C composites under different experimental conditions

This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B4C particles were blended in a high energy ball mill. Cold compacted Al7075/B4C blends were pressed at semisolid state. The effects of the size of the matrix（20, 45 and 63 μm）, reinforcing volume fraction（5%, 10% and 20%） and semisolid compaction pressure（50 and 100 MPa） on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B4C particles（45 μm） were distributed within the small particles（20 μm） of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10%（volume fraction）. Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20%（volume fraction） 45 μm B4C powder pressed under 100 MPa exhibited the highest values of hardness（HV 190） and compressive strength（336 MPa）.

颗粒形貌及热处理对SiC_p/2024Al复合材料性能的影响

采用粉末半固态触变成形工艺制备了SiCp体积分数为60%的2024Al复合材料。研究了SiCp形貌及热处理对复合材料性能的影响。结果表明,经表面整形的SiCp制备的复合材料增强体颗粒均匀弥散地分布在铝基体上,其致密度能达到99.97%。对复合材料进行去应力退火和T6热处理后,复合材料得到最佳综合性能,其抗弯强度和硬度得到明显提高,与复合材料热处理前相比,分别提高了47.5%和57.7%。复合材料的断裂整体表现为SiCp的解理断裂,基体呈现出撕裂。对SiCp整形和复合材料退火及T6热处理后降低了复合材料的热膨胀系数,分别达到(4.85~8.51)×10^-6、(4.86~8.32)×10^-6℃^-1。经改进后的H-J模型可以更好地适用于混合增强和双峰粒径分布的情况。对SiCp整形和复合材料退火及T6热处理后显著提高了复合材料的热导率,分别达到195、206W·m^-1·K^-1。