铝铅合金的半固态成形工艺研究

利用双筒式机械搅拌装置制备铝铅系难混溶合金。双筒式机械搅拌装置由一对带有螺纹的内外桶构成,当内筒旋转时在内外桶的缝隙形成剧烈的剪切应力场。通过控制桶的转速和内外桶缝隙可以获得0～153.45s-1的剪切速率,温度在0～1000℃之间任意调节。通过计算分析:铝铅合金的半固态流变成形温度区间为570～630℃,同时得到了铝铅合金的固相率随温度变化的关系曲线。此外还确定了转速与剪切速率的关系。并在温度为594℃,固相率为0.5时,采用不同的剪切速率制备铝铅合金锭料,来验证计算结果。理论和试验结果表明,通过机械搅拌的半固态成形技术,可以制备出铅颗粒均匀、弥散分布的铝铅难混溶合金。     

基于CA-CCA方法定量解析AZ91D镁合金半固态固相率的研究

针对镁合金半固态成形工艺中,初始固相率难以精确确定的问题,以传热学模型和CA-CCA原理为基础,设计制作了一套研究半固态固相率的实验装置,通过实测降温过程中的温度-时间曲线,进行数值解析,实现了半固态固相率与温度定量关系的求解.结果表明,AZ91D合金的固相率对温度的变化极为敏感,且呈非线性关系.当固相率从20%上升至30%时,温度变化仅为6℃左右;而固相率从30%上升至40%时,温度变化仅在7℃左右.因此,对温度进行定量控制是制备高性能AZ91D合金的关键技术之一.     

剪切力下半固态Sn-52Bi合金组织演变与塑性的研究

采用机械搅拌的半固态铸造技术制备Sn-52Bi合金,探索了不同固相率下剪切力和作用时间对半固态Sn-Bi合金组织和塑性的影响。结果表明,在近液相线的146℃(固相率为4%),搅拌速度为320 r/min和搅拌6 min的工艺条件下,制备出分布均匀、直径约10μm球状初生相的半固态Sn-52Bi合金,其伸长率为31.3%,与在180℃下的合金金属熔液直接水冷凝固而成的相比提高了74.8%。随着剪切力作用时间的延长和半固态合金浆料中固相率的增加,半固态浆料的初生相易发生团聚,所制备的半固态Sn-Bi合金初生相为分布不均的蔷薇形或椭圆形,合金伸长率下降。     

保温参数对A356铝合金半固态组织的影响

采用自孕育法制备A356铝合金半固态浆料,对比分析了半固态金属型铸造与传统金属型铸造的组织,研究了不同保温时间及保温温度对A356半固态浆料水淬组织的影响。结果表明,A356铝合金采用自孕育法进行半固态流变铸造可获得初生相分布均匀的非枝晶组织;A356半固态浆料在保温3min时初生颗粒的形状因子最接近于1,而且颗粒平均尺寸相对较小,因此,保温3min的组织为较理想的流变成形组织;保温温度的高低直接影响最终浆料固相率的高低。固相率过高(50%以上),初生颗粒的合并现象严重,使组织恶化;固相率过低(15%以下),浆料接近全液态,达不到半固态成形利于补缩的效果。适合A356合金的半固态保温温度为600~610℃。     

剪切力对半固态Sn-Bi合金的组织演变与塑性的影响

采用机械搅拌半固态铸造技术制备Sn-62Bi合金,通过XRD、EDS等测试方法探索了不同固相率下剪切力和作用时间对半固态Sn-Bi合金组织和塑性的影响。结果表明:在半固态温度145℃、搅拌速度为500 r/min和搅拌时间为15 min的工艺条件下,制备出分布均匀、尺寸约30μm块状铋初生相的半固态Sn-62Bi合金,拉伸试验下的伸长率为39.9%,与在180℃下的合金金属熔液直接水冷凝固而成的试样相比,其伸长率提高了283.3%。当搅拌温度为150℃时,随着搅拌时间的延长,块状初生相Bi相相互摩擦和碰撞破碎,初生相的尺寸减少,分布较均匀,所制备的半固态Sn-62Bi合金的伸长率得到改善。     

二次加热过程中半固态AZ31镁合金的显微组织演变

利用波浪形倾斜板振动技术制备AZ31镁合金半固态坯料,获得较为理想的球形或近球形晶粒组织。结果表明:随二次加热温度的升高和保温时间的延长,半固态组织中的液相体积分数增大,固相逐渐长大并球化;AZ31镁合金580℃和610℃时二次加热组织均不适合半固态触变成形;适合触变成形的二次加热最优工艺为590℃保温40～60 min、或者600℃保温30 min;此条件下获得的平均晶粒直径为58～61μm,固相率为87%(体积分数)左右。晶格扩散机制对二次加热原子扩散起主导作用,是造成合金固相颗粒尺寸变化的根本原因;固液界面张力是造成颗粒形状球形或近球形变化的重要原因。     

铝-7石墨复合材料的半固态加工

采用电磁机械复合搅拌法制备了铝-7石墨的半固态浆料,研究了常规铸造条件下浆料的固相率对铸锭中石墨颗 粒分布的影响,得到了合理的铝-7石墨复合材料半固态加工工艺条件。     

加热工艺对冷轧6061合金半固态显微组织的影响

基于SIMA法,采用冷轧+半固态热处理工艺制备出6061铝合金半固态坯料。研究了半固态加热温度和保温时间对6061铝合金半固态坯料显微组织的影响。结果表明:随半固态加热温度的升高,α-Al固相颗粒的球形率增大,液相率升高;保温时间在0~15 min内,随保温时间的延长,α-Al固相颗粒越圆整、分布越均匀,液相率越高;当保温时间超过15 min后,α-Al固相颗粒尺寸逐渐增大,颗粒有簇聚的趋势,而液相率变化不明显;优化的加热工艺参数为630℃保温15 min,可获得6061铝合金半固态坯料理想的显微组织。     

搅拌工艺参数对SIMA法半固态AZ91D镁合金组织的影响

采用自行设计制造的半固态镁合金机械搅拌装置，制备了镁合金半固态浆料，研究了搅拌工艺参数对半固态镁合金组织的影响。结果表明：镁合金半固态等温搅拌温度在570～580℃，搅拌时间为6～9min时，获得的组织均匀细小。搅拌时间过长，晶粒尺寸反而有所增大。搅拌温度影响固相率，从而也影响到固相晶粒的圆整度。     

半固态铝-7石墨比重偏析控制的数值模拟

根据有限元体积法建立了流体方程组,并建立了固液两相双流体模型.利用流体模拟软件FLUENT对搅拌器中固液两相流的混合进行了数值模拟,得到了半固态铝-7石墨合金在600℃时机械搅拌情况下消除合金偏析时流体的流动特性和湍流动能分布,模拟出了三种温度下搅拌720 s后石墨分布的图形,同时确定600 ℃是所选的三个温度中石墨颗粒偏析程度最小的温度,也得出了时间与搅拌温度的关系.     

铸造Al-Pb轴承合金的组织和性能

利用一种新的搅拌铸造技术生产系列铸造铝铅合金,含铅量的变化范围在ω（Ｐｂ）－０￣２５％,试验中,研究了铸态铝铅合金的显微组织和力学性能。结果表明,在研究的含铅量范围内,铸态合 硬度、抗拉强度和虎率都随铅的质量分数的增加而下降。断口分析表明,随质量分数的增加断口特征逐渐由塑性向脆性转变。而摩擦磨损性能随铅的质量分数的增加有一最佳值,即铅的质量分数为１５－２０％时,其磨损量和摩擦系数最小。     

"挤压-轧制"对Al-Pb合金板材微观结构与力学性能的影响

研究了Al-Pb合金制成板材过程中“挤压-轧制”对板材微观结构与力学性能的影响。结果显示，Al-Pb合金变形前Pb分布在枝晶间隙或“嵌”在基体中；合金热挤压成板材后，合金颗粒内部的Pb细化，但变形颗粒新生表面的Pb粗化，在随后的轧制变形及热处理时难以消除“Pb粗化”造成的遗传影响。合金板材的铝基体发生再结晶前，力学性能主要受Pb形貌影响；发生再结晶后，力学性能主要受基体微观结构影响。     

触变注射成形AZ91D合金组织和拉伸断裂特性研究

通过不同工艺制备的合金的组织特点和性能变化,研究了触变注射成形AZ91D合金的拉伸断裂行为。结果表明,典型触变注射成形AZ91D合金的室温组织主要由未熔固相α-Mg和液相急冷组织构成。未熔固相有类球状、不规则状、包裹液相和内部小液池等4种形态。液相急冷组织包含初生α-Mg固相和共晶相,初生固相较规则,尺寸较小,主要受液相的过冷度影响。当组织变化不大时,孔隙率对合金性能的影响最大,而当孔隙率变化不大时,组织的变化对性能的影响较大,固相率较低和初生固相较细小的试样的力学性能较好。试样拉伸时裂纹主要沿着未熔固相与液相的界面或初生固相与共晶的界面扩展。当固相率较高时,裂纹大部分沿着未熔固相与液相的界面扩展,试样的性能较低;而当固相率较低时,裂纹大部分沿着初生固相与共晶相的界面扩展,并通过β相的桥接进行拓展,性能较好。     

均匀化温度对K465合金组织与性能的影响

通过对K465镍基高温合金不同温度均匀化处理后的组织形貌观察及力学性能测试,研究了均匀化温度对K465合金显微组织及力学性能的影响。结果表明,在γ′相固溶温度以下(1160 ℃)均匀化后,γ′相尺寸较铸态大;在接近γ′相固溶温度(1210 ℃)均匀化后,合金中的γ′体积分数约为54%,尺寸均匀且立方化程度较高;在1260 ℃均匀化后,γ′相呈小颗粒状弥散分布,并且晶内出现胞状结构。随着均匀化温度的升高,合金的枝晶偏析情况减弱,碳化物由发达的骨架状逐渐转变为短棒状以及块状。热处理工艺为1210 ℃×4 h时合金具有最佳的综合性能。     

球磨法制备Fe-1％C纳米晶及其热稳定性

微观应变的存在,获得的Fe-C纳米晶具有自发长大趋势.采用差热分析(DSC)手段研究不同等温条件下Fe-C纳米晶的热稳定性,结合晶粒长大热力学和动力学理论,求得晶界扩散激活能及稳定晶粒尺寸等参数,并分析讨论Fe-C纳米晶的晶粒稳定机制.     

机械合金化制备的Al-Pb-Cu合金结构与摩擦性能

用机械合金化方法制备了Al-Pb-Cu合金。X射线衍射（XRD）和扫描电镜（SEM）分析表明，随机械合金化的进行，Al-Pb-Cu合金中相继有Cu9Al4和CuAl2相形成，在随后的烧结过程中，CuAl2相农渐增加，而Cu9Al4相逐渐消失，最终获得了在Al基体上弥散分布为Pb相和CuAl2相的组织，与Al-Pb二元合金相比，Cu的加入在一定程度上抑制了Pb相的长大，摩擦磨损性能测定表明，Al-Pb-Cu合金的摩擦磨损性能比相同方法制备的Al-Pb二元合金有了较大提高，当Cu含量（质量分数）为4．5％时，合金的耐磨性最佳。     

Effect of heat treatment on electrochemical behaviour of binary aluminium model alloys

In order to understand the role of various trace, impurity and alloying elements on the electrochemical activation of aluminium in chloride solution, binary alloys of type Al-Pb, Al-Bi, Al-In, Al-Sn, Al-Mg and Al-Zn were investigated by use of electrochemical and surface-analytical techniques. Al-Pb and Al-Bi alloys were electrochemically activated as a result of high temperature heat treatment. However, alkaline etching or mechanical polishing significantly reduced the activation. Alloys Al-In and Al-Sn were electrochemically activated regardless of surface condition. The activation of Al-Pb alloys is attributed to enrichment of lead, presumably in metallic form, at the metal-oxide interface by segregation and diffusion along the grain boundaries. In the presence of chloride, lead destabilises the surface oxide, giving rise to unexpected oxidation of the underlying aluminium at potentials well below the pitting potential. It is suggested that the resulting detachment of the Pb from the aluminium surface causes repassivation. Aluminium is not activated by Mg or Zn as a result of high temperature heat treatment.     

Friction and wear characteristics of hot-extruded leaded aluminum bearing alloys

The friction and wear characteristics of hot-extruded Al-Pb alloys with lead contents in the range 0–25 wt.% and as-cast Al-Pb alloys with lead content of 20 wt.% were investigated under dry-sliding conditions using a pin-on-disc test machine. It was found that hot extrusion greatly decreased the porosity that was caused by powerful stirring and considerably improved the mechanical properties of stircast Al-Pb alloys, including wear behavior. The coefficient of friction and wear rate decreased with increasing lead content, and especially the antiseizure property of hot-extruded Al-Pb alloys containing 20 wt.% and 25 wt.% lead were improved remarkably. Optical observation revealed that the reason for this was the formation of a black compact film of lubricant that covered almost the entire worn surface of specimens at a highly applied load level. This film is a mixture of different constituents containing Al, Fe, Si, O, and Pb.     

Microstructure evolution and mechanical properties' improvement of NiAl–Cr(Mo)–Hf eutectic alloy during suction casting and subsequent HIP treatment

A NiAl–Cr(Mo)–Hf eutectic alloy was prepared by suction-casting technique and subsequently hot isostatic pressing treatment. Microstructure and mechanical tests were performed and the results revealed that the suction-cast alloy possessed fine NiAl/Cr(Mo) lamellar, large area fraction of eutectic cell and semi-continuously distributed Ni₂AlHf phase at the cell boundaries. After the HIP treatment, the Ni₂AlHf particles became fine and distributed evenly in the alloy. Moreover, some of the Ni₂AlHf particles along the eutectic cell boundaries were transformed into Hf solid solution phase. Compared with the conventionally cast alloy, the room-temperature compressive ductility and strength of the suction-cast alloy attained significant improvement. In addition, the room-temperature ductility and elevated temperature strength of suction-cast alloy were markedly enhanced by HIP treatment.     

Hot-roll bonding of Al-Pb bearing alloy strips and hot dip aluminized steel sheets

In this paper, the basic bonding mechanism between two materials of practical importance is identified. One of the materials is carbon steel, which has been aluminized on its surface by immersion in molten aluminum. This step produced a Fe-Al intermetallic compound layer. The other material is an Al-Pb alloy (a bearing material). The two materials were hot roll bonded together. It was found that the Fe-Al intermetallic compound broke into discontinuous blocks during the hot rolling operation. The block of intermetallic compound remained bonded to the steel. The overall bond between the Al-Pb strip and the steel strip resulted from two different bonds. The Al-Pb strip and the Fe-Al intermetallic compound (this is called the “block bond” in this paper) and the Al-Pb strip and the bare steel surface in the area where the block separated from the steel substrate (this is called the “blank bond” in this paper). The effects of dipping time and thickness of the intermetallic layer as well as the fractional amount of blank interfaces on the interfacial bonding strength were investigated. The total bonding strength mainly depended on that of blank interfaces and the area fraction of blank interfaces. There was a linear relationship between total bonding strength and fraction of blank interfaces. The bonding strength of blank interfaces was four times as high as that of the block interfaces. The fraction of blank interfaces increased with increasing intermetallic thickness values below 73 μm and decreased beyond 73 μm.