粉状铝基钎料的高频钎焊工艺研究

介绍了粉状铝基钎料的制备方法,探讨了粉状铝基钎料的工艺性能。从表面张力的角度出发,讨论了粉末粒度、氧含量、加热速度、加热均匀性、钎料钎剂比例等因素对高频铝材钎焊工艺和性能的影响。结果表明:用粒度在150~180μm的粉状铝基钎料钎焊铝材,其钎焊剪切强度较高;加热速度较快、加热盘温度均匀的钎焊效果较好;钎料钎剂的比值在10∶8~10∶10范围钎焊效果较好。     

稀土元素对低温铝基钎料性能影响的研究

本文研究了稀土元素Ｙ、Ｃｅ对Ａｌ－Ｚｎ－Ｃｕ－Ｓｉ系列低温铝基钎料的熔化温度、钎焊工艺性、电极电位及其接头的机械性能及抗腐蚀性能的影响。结果表明：少量Ｙ、Ｃｅ的加入，对钎料的熔化温度影响不大，能提高钎料的钎焊工艺性；稀土Ｙ、Ｃｅ能细化晶粒，改变组织的分布状态，不改变钎料的电极电位，但却提高了钎焊接头的机械性能和抗腐蚀性。     

高精度软钎料箔带的研制

介绍了一种高精度汽车水箱专用软钎料箔带的研制过程，通过确定合适的合金成分、工艺流程和工艺条件，使开发的水箱软钎料箔带性能指标达到国外同类产品水平。     

SiC纤维增强SiC陶瓷基复合材料与40Cr钢的连接

采用Ag-Cu-Ti钎料对化学气相渗积方法制造的SiC纤维增强SiC陶瓷基复合材料与40Cr钢进行了真空钎焊。对接头的微观组织进行了观察，研究了不同钎料厚度及中间层对接头的影响。结果表明，利用Ag-Cu-Ti钎料可以实现二者的连接；中间层Cu以及钎料中的Ti、Ag、Cu有利于提高连接强度；不同钎料厚度影响连接强度，加两层钎料时，接头具有最高室温强度。     

BNi73CrSiB-40Ni钎料的钎焊工艺性能及接头组织研究

为了解BNi73CrSiB—40Ni钎料的钎焊工艺性能，对该钎料进行了表面质量分析、化学成分分析及DTA测试，以GH3044，ЭП708高温合金为母材，研究了钎料的铺展面积、填充间隙能力、漫流长度等钎焊工艺性能。结果表明：该钎料具有良好的流动性能、良好的填充间隙性能，适宜大间隙和不等间隙接头的钎焊。该钎料的钎焊接头中有大量的固溶体组织，不同于常用钎料BNi82CrSiB的钎焊接头的组织。     

新型水性铝焊膏的研究

铝焊膏分油性和水性,水性铝焊膏由铝钎料、铝钎剂和水性成膏体组成,通过对这三组分定性、定量的研究,尤其将研究重点放在水性成膏体方面,研制出了新型水性铝焊膏。该水性铝焊膏同样适合于铝-铝、铝-铝合金、铝-不锈钢的焊接,具有简单、方便和环保的特点。     

合金元素对Sn-9Zn基无铅钎料润湿性和组织的影响

研究了分别添加混合轻稀土、磷和铋对Sn-9Zn共晶合金在铜基上的润湿性能及对钎料内部显微结构和钎料/铜界面的影响。研究结果表明:Bi、RE和P都能有效地改善Sn-9Zn基合金钎料在铜基上的润湿性;且添加RE和P对钎料/铜界面无明显的影响,也不改变Sn-9Zn钎料内部的扫把状共晶结构;而添加Bi促进了Sn-9Zn合金中锌的富集析出。     

BNi2粉末钎料的性能研究

对用气雾化工艺生产研制的BNi2钎料粉末化学成分、颗粒形态、粒度分布、氧含量及熔点进行了检测，并对其微观组织和结构进行了分析。结果表明：BNi2钎料粉末呈球形。成分稳定，氧含量低，组织均匀．各项性能满足钎焊工艺要求。实现了BNi2钎料粉末的产业化和国产化目标。     

钛基钎料钎焊石墨与TZM合金接头组织和性能研究

研究了钛基钎料钎焊石墨与TZM合金的钎焊组织。结果表明，使用钛合金箔为钎料能很好润湿石墨和TZM母材，通过界面反应和TLP扩散连接获得良好的钎焊组织。接头组织主要分为两层：Ti-TiC和Ti-Mo固溶体。热震循环试验证明接头再熔化温度高于1400℃，承受热应力而不失效。接头剪切强度为14．1MPa。     

温度时效对SnAgCuLa/Cu接头金属间化合物层形貌和厚度的影响

SnAgCu系无铅钎料是颇具潜力的SnPb系钎料替代品,但该钎料在钎焊过程中会在钎料/铜基板界面生成具有一定厚度的金属间化合物层。锡基钎料钎焊接头的服役温度一般高于常温,在服役温度下,钎焊接头的金属间化合物(IMC)层的形态和厚度均会发生改变。本实验采用Sn-3.8Ag-0.7Cu钎料,向其中添加不同量的La(x=0,0.2,0.5),比较各成分钎焊接头常温IMC层厚度,并将不同成分钎料的接头分别在75℃、125℃、160℃温度时效处理24h后,观察界面IMC层的形态并计算尺寸。结果表明,适量La的添加对界面IMC层的生长具有抑制作用;当La的添加量为0.5wt.%,与未添加La时相比,常温条件下,其IMC层厚度下降了41.51%;温度时效后,接头IMC层厚度与时效温度近似呈线性关系,且随着La的增加,其比例系数减小。     

挤压铝型材表面拉毛形成原因分析

采用直读光谱仪、扫描电镜等设备,通过分析合金成分、挤压工艺、铸棒表面质量对型材拉毛缺陷的影响,研究拉毛形成的原因。结果表明,拉毛缺陷前端有明显沿挤压方向台阶状划伤痕迹,收尾瘤状颗粒形状不规则;成分与基体接近,其周围分布Fe、Si、C、O含量高的异质颗粒;挤压速度过快,挤压出口温度过高,铸棒表面粗糙都会加剧表面拉毛的产生。     

Modeling the dynamics of magnetic semilevitation melting

In semilevitation melting, a cylindrical metal ingot is melted by a coaxial a.c. induction coil. A watercooled solid base supports the ingot, while the top and side free surface is confined by the magnetic forces as the melting front progresses. The dynamic interplay between gravity, hydrodynamic stress, and the Lorentz force in the fluid determines the instantaneous free surface shape. The coupled nonstationary equations for turbulent flow, heat with phase change, and high-frequency electromagnetic field are solved numerically for the axisymmetric time-dependent domain by a continuous mesh transformation, using a pseudospectral method. Results are obtained for the two actually existing coil configurations and several validation cases.     

宽规格汽车板沉没辊印成因分析及控制技术

针对某2 230冷轧镀锌宽规格汽车板出现的沉没辊印缺陷问题,采用SIAS带钢表检系统和ZEISS扫描电镜对沉没辊印的形状进行了有针对性的宏观描述,对扫描电镜下出现的微观特征进行分析,最终确定沉没辊印缺陷的形成过程。通过沉没辊改善沟槽表面质量、沉没辊表面沟槽改造、冷却塔带钢跑偏等多方面调整措施,有效地解决了锌锅沉没辊印问题,取得了显著的应用效果。     

Trials for Reducing Depth of Oscillation Marks in Continuous Casting

Improvement of surface defects in a continuously cast slab or billet is important for saving surface scarfing and for carrying out direct rolling. Deep oscillation marks, one type of the surface defects, sometimes cause surface cracking and positive segregation. In this study, the mechanism by which oscillation marks are formed was investigated by using a continuously cast simulator, which is a billet‐type machine. Then attempts were made to reduce the depth of oscillation marks by two methods in which electromagnetic force, which is the most effective means for reducing depth, was not used. The two methods were use of an adiabatic board for preventing solidification of a meniscus and the use of a board for suppressing the flow of flux. Overlapping of a molten metal on a meniscus resulted in formation of oscillation marks in tin. On the other hand, bending of a solidified shell also resulted in formation of oscillation marks in a tin‐lead alloy. The depth of the oscillation marks formed by the overlapping mechanism was greater than that formed by the bending mechanism. Both mechanisms depended on the strength of the solidified shell. Therefore, two trials to reduce the depth of oscillation marks formed by the overlapping mechanism were carried out. In one trial, an adiabatic board was inserted into the molten metal. Reduction in depth of the oscillation marks reduced up to about 86% was achieved when high viscosity flux was used. However, the adiabatic board was not effective when low viscosity flux was used. In the other trial, a board was inserted into a molten flux layer with a depth of 10 mm in depth in order to suppress the flow of the flux and to change the direction of flux flow, and the depth of oscillation marks was reduced by about 33%. Therefore, both of these methods are effective for reducing the depth of oscillation marks in a continuously cast billet.     

Experimental study of oscillation mark depth in continuous casting of steel

Abstract

Mould oscillation is needed to reduce friction and thus prevent sticking and breakout of the liquid metal during casting. However, this oscillation is known to cause surface defects in the solidified steel slabs, so called oscillation marks. In this paper, the depth and the depth variation of these oscillation marks were studied using a two-level full factorial experiment (2) with four additional centre point runs. Four factors were studied: stroke length of the mould, oscillation frequency, motion pattern (strip factor) and casting speed. The stroke length affected the depth of the marks the most, where larger strokes created deeper marks. The interaction between the oscillation frequency and the strip factor of the mould also affected the oscillation mark depth. The oscillation mark depth variation was also increased by increased stroke lengths and at higher oscillation frequencies. The largest effect on the oscillation depth variation was found for the interaction between the stroke length and the oscillation frequency.     

Redistribution of particles during casting of composite melts: Effects of buoyancy and particle pushing

When a melt containing a dispersion of second phase particles is solidified, the initial distribution of the particles can change due to three phenomena, namely, buoyant motion of the particles, pushing of the particles by the moving solidification front, and by convection currents in the melt. This paper presents a computer simulation model using which, the net redistribution due to the combined effect of the first two phenomena can be predicted. the existing theory for calculating the critical velocity for particle pushing is extended to include the effect of the buoyancy force and a numerical correlation is developed for easy calculation of the critical velocity. This correlation is incorporated into a computer programme which tracks the position, velocity and direction of the solidification front as well as the position of each particle in the melt as a function of time. The final positions of the particles describe the distribution of the particles in the solidified material. Predicted distributions for various heat extraction rates and particle sizes are presented for a system of silicon carbide particles in a pure aluminium melt solidifying unidirectionally as well as multidirectionally in cylindrical moulds. It is shown that for any heat extraction rate there is an optimum particle size which gives the maximum uniformity of distribution in the solidified material.     

Numerical treatment of rapid solidification

Techniques are reviewed for describing crystal nucleation and subsequent advance of the crystallization front in metallic melts under the range of conditions generated during rapid solidification processing. The selection of appropriate boundary conditions in these cases is discussed, with particular reference to coupling between the undercooling at and the velocity of the growth front. It is emphasized that, although solute redistribution may occur, the process is normally under heat flow control and techniques for treating the associated phenomena are described. Some illustrative theoretical curves are presented for unidimensional heat flow toward a massive substrate, while the relevance to other processes, such as gas atomization, is periodically noted. Some attention is devoted to recalescence (removal of the undercooling) of the growth front as a result of latent heat evolution and the degree to which this might be counteracted by external cooling. A rationale is presented enabling the conditions under which recalescence could be arrested (thus permitting strongly enhanced crystal growth rates) to be estimated for different base metals. Mention is made of solute redistribution phenomena during recalescence of alloys. Finally, some implications of the data presented are briefly discussed in practical terms.     

渗氮层的微观结构对渗层脆性的影响

利用Ｘ射线衍射仪和透射电镜研究了离子渗氮层和普通气体渗氮层的微观结构及其对渗层脆性的影响。结果表明,离子渗氮化合物层中γ′相的含量比普通气体渗氮的要多,且γ′相晶粒较小;离子渗氮扩散层中的碳化物呈粒状,而普通气体渗氮扩散层中的碳化物呈断续的长条状,且分布有一定的方向性。这是离子渗氮的渗层脆性低于普通气体渗氮的重要原因。     

冷轧薄板线状缺陷的工艺控制

针对某钢厂结晶器液面翻腾导致卷渣严重与中间包过热度控制缺乏依据为背景,对结晶器内流态和过热度对表面质量影响开展研究。文献调研与大量线状缺陷电镜分析发现,导致线状缺陷的夹杂物主要是氧化铝和保护渣,且引起线状缺陷的大尺寸夹杂物主要分布在铸坯表层5mm内。减少吹氩量与增大浸入深度可提高双股流比例,基于水模型和工业试验,提出控制临界吹气量得到双股流。应用该结果后,消除了结晶器液面翻腾现象,提高中间包过热度可减少钩状坯壳深度与铸坯表层夹杂物数量。综合考虑钢水洁净度提出冷轧薄板钢过热度控制在25~40℃。基于以上措施,该厂炼钢缺陷导致降级率由1.1%降至0.6%。     

Influence of atomising gas pressure on 63A solder powder in supersonic atomisation

Abstract

The atomising gas pressure is one of several important process parameters that affect the characteristics of the powder particles. The work analyses qualitatively the influence of the atomising gas pressure on 63A solder alloy fine powders. Also studied was the mechanism of the effect of the atomising pressure on the base of the air dynamics through the atomising 63A solder alloy experiment with different atomising pressures on the supersonic nozzle. The results indicate that 63A solder alloy fine powders may be attained, which can satisfy the SMT application requirement when the atomising gas pressure is at 0.7 MPa.