Intermetallic compounds formed during brazing of titanium with aluminium filler metals

The effect of aluminium filler metal composition on the formation of AI-Ti intermetallic compounds was investigated in brazed aluminium-to-titanium (Al/Ti) joints and titanium-totitanium (Ti/Ti) joints. The clearance filling ability was also studied. In Ti/Ti joints, the thickness of the intermetallic compound layer was strongly dependent on the aluminium filler metal composition, whereas the clearance filling ability was independent of the composition. The maximum intermetallic compound layer thickness was observed in 99.99% highly pure aluminium filler metal; therefore all additional elements reduced the layer thickness. Above all, the addition of 0.8% Si greatly reduced the thickness. After brazing at 680° C for 3 min, the intermetallic compound formed by Al-0 to 0.8% Si filler metal was found to be of type Al₃Ti. Other compounds, of types Ti₉Al₂₃ and Ti₇Al₅Si₁₂, were also found in joints brazed by Al-3 to 10% Si filler metals. AI-0.8% Si filler metals maintained a higher joint strength than pure aluminium filler metal under brazing conditions of high temperature and long heating time. In Al/Ti joints, AI-Cu-Sn and AI-Cu-Ag filler metal mainly formed Al₃Ti, and Al-10Si-Mg filler metal mainly formed Ti₇Al₅Si₁₂ at the brazed interface of the titanium side after brazing at 600 to 620° C.     

Formation of microlayers of clad residue on aluminium brazing sheet during melting and resolidification in brazing process

Abstract

The present paper is devoted to an analysis of clad residue formation during a controlled atmosphere brazing (CAB) process applied to composite aluminium brazing sheets. Evolution of the microstructure of the clad residue, and in particular the mass of resolidified clad formed, were studied. Observations confirmed that, even under optimal brazing conditions, a residue layer (formed away from the joint zone) always appears after brazing. It was established that the peak brazing temperature plays an important role in the process responsible for formation of the residue mass. However, dwell time at the peak brazing temperature does not have a significant influence on clad residue mass accumulation beyond its known influence on substrate dissolution and core metal erosion in the joint zone.     

High-performance joining technology for aluminium matrix composites using ultrasonic-assisted brazing

High-performance aluminium matrix composite joints were fabricated using a new joining technology assisted by ultrasonic vibration. The performance of the joints was close to that of the parent materials. The microstructure and the mechanical performance were found to be systematically dependent on the volume fraction and the distribution of reinforcement particles in the bond region. The authors believe that this study can be generalised to the bonding of other ceramic-reinforced metal matrix composites.     

New filler metals and process for fluxless brazing of aluminium engineering alloys

Abstract

Many high strength aluminium engineering alloys cannot be joined by brazing because they either degrade or melt at the temperature at which commercially available aluminium brazes are used. A brazing process suitable for joining aluminium engineering alloys has been developed employing two novel low melting point brazes. The brazes are available as ductile foil preforms. The process is fluxless and no post-joining cleaning treatments are necessary. The aluminium components and the brazing foil require a simple chemical treatment before use. The brazing process is tolerant and can be satisfactorily implemented by heating to a temperature of 510–550°C, maintained for a period of 5–45 min, in either vacuum or a furnace chamber that is purged continuously with nitrogen gas. The joints exhibit high strength and adequate resistance to corrosion for most applications. Some promising new applications for aluminium brazing technology based on this new process are described.

MST/3183     

Ultrasonic brazing of aluminium matrix composites assisted by operation of melting and squeezing

Abstract

Particle-reinforced aluminium metal matrix composites were ultrasonically brazed. In situ compositing technology of a particle-reinforced bond is described in this article. The joints with lower strength showed a structure of composite material/bond metal/composite material after ultrasonic brazing. The double liquid–solid zones in the base material close to the bond were fabricated by means of melting the base materials at a relatively higher temperature. Then pressure was applied to the samples, the double liquid–solid zones and the bond were mixed with each other and a particle-reinforced bond formed. The microstructure of the particle-reinforced bond is very similar to that of the base composite materials. The shear strength of the bonds was improved dramatically.     

Ultrasonic brazing of high fraction volume of SiC particulate reinforced aluminium matrix composites

Abstract

The ultrasonic brazing of 55 vol.-%SiC_p/A356 composites in air has been investigated. When the ultrasonic vibration is applied for 0·5 s, the oxide layer is still continuous at most places between the filler metal and the composites. As the ultrasonic action time increases, the oxide film sufficiently disappears in the bond region, resulting in the complete wetting of Zn–Al alloy with the composites and the significant mass transfer between the SiC/A356 and the Zn–Al alloy is observed. As the dissolving of the composites on the surface, the SiC particles in the base materials get into the bond metals in which reinforcements are distributed uniformly. The shear strength of bonds increases with the ultrasonic acting time.     

大型真空铝钎焊装备--主要技术参数设计与控制

我国自行研制拥有完全自主知识产权的大型真空铝钎焊装备已完成了工业产业化推广.文章介绍了该装备的主要技术参数确定方法和依据.     

Short-time heating of a body by a radiant flux

An approximate computation is proposed for heating a massive optically dense body in a furnace with predominant thermal radiation mechanism.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 1, pp. 93–97, January, 1986.     

Multistep induction heating regimes for thixoforming 7075 aluminium alloy

Abstract

Thixoforming involves processing alloys with a spheroidal microstructure in the semisolid state. Commercially it is applied to conventional casting alloys, and one of the scientific challenges is to extend its application to high performance aluminium alloys such as 7075. Aluminium alloy 7075 is readily available in extruded form, and one route to a spheroidal microstructure is to reheat extruded material into the semisolid state to obtain recrystallisation, with the liquid penetrating the recrystallised boundaries. Here this route has been followed, but it has been found that the presence of pinning particles in the microstructure inhibits recrystallisation. To overcome this, a multistep induction heating regime has been developed consisting of a 1 min hold at 475-500 °C, a 1 min hold at 575-600 °C and a shorter 20 s hold for the final step at 620 °C.     

Dissolution of TiAl alloy during high temperature brazing

An analytical model has been established to evaluate the thickness of the dissolution layer of base metal in a liquid brazing filler metal during a high temperature brazing process. The model was validated by a study of brazing of a TiAl alloy to a 42CrMo steel. Peak brazing temperatures were within a range of 1103–1203 K. The margin of deviation between predicted and experimentally determined dissolution thicknesses is within the range of 1–14 %, thus supporting the validity of the model well.     

Reactive brazing of aluminium to aluminium-based composite reinforced with alumina borate whiskers with Cu interlayer

The microstructure of the joints formed by vacuum reactive brazing of aluminium to aluminium-based composite, with a copper interlayer was investigated. Al-Cu eutectic (Al₂Cu + Al) was the predominant phase at the interface. The maximum shear strength of the joint was 85 MPa. The results show that reactive brazing with a Cu interlayer can be used successfully for joining aluminium and aluminium-based composites reinforced with alumina borate whiskers.     

Radiative heat flux absorbed by a fluidized bed in radiative heating

An equation is derived for the heat flux absorbed by a fluidized bed in radiative heating.     

The heating of materials by a concentrated energy flux under volume absorption

An analysis is represented for the process of heating a massive body by concentrated energy flux with volume absorption taken into account. The boundaries of applicability are determined for models of surface and volume absorption. The temperature fields are computed and simple analytical dependences are obtained for the temperature at the center of the heating spot.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 5, pp. 846–849, November, 1990.     

The effect of heating shot peened sheets and thin plates of aluminium alloys

2024, 7075 and 7475 aluminium alloy sheet and thin plate specimens shot peened to various intensities and subsequently exposed for periods up to 500 h at temperatures up to 120 ° C showed significant decreases in the level of residual stress induced by the shot peening and significant changes in geometrical contour even for exposure temperatures as low as 80 ° C. The higher the intensity of the shot peening, the higher the temperature of exposure and the longer the period of exposure, the greater was the relief of residual stress. After 40 h at 120 ° C the level of residual stress was reduced by more than 60%. Specimens formed to a given curvature by shot peening tended to straighten out on exposure at elevated temperatures. Such significant effects were obtained at temperatures as low as 80 ° C, these increasing with duration and temperature of exposure. The results and the possible effect of a tendency to change the contour of a flight component in service are discussed. Metallurgical ameliorative measures for some of these effects are demonstrated.