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THE PROPERTIES AND MICROSTRUCTURE OF AlTi6/Al2O3 JOINTS DOI:10.15199/67.2015.4.1


  The influence of the titanium addition into aluminium on the bond strength properties and structure of interface of the AlTi6/Al2O3 joints was investigated. The bond strength of the metal/Al2O3 joints was determined by the push-off test. Addition of 5.9 wt.%. Ti to Al caused the reduction of shear strength of the AlTi6/Al2O3 joints. The investigations by mean of electron microscopy equipped with a spectrometric system for microanalysis of the chemical composition revealed TiAl3 phases formed at the AlTi6/Al2O3 interface. Oxygen was detected in some areas of TiAl3 phases. Finally, this structure of the AlTi6/Al2O3 interface was responsible for lower bond strength comparing to properties of the Al/Al2O3 joints. Keywords: AlTi6/Al2O3 joint; shear strength, interface WŁAŚCIWOŚCI I MIKROSTRUKTURA POŁĄCZENIA AlTi6/Al2O3 W pracy przedstawiono badania dotyczące wpływu dodatku tytanu do aluminium na wytrzymałość na ścinanie oraz mikrostrukturę połączenia AlTi6/Al2O3. Wyniki wykazały, że dodanie tytanu do aluminium wpływa na obniżenie wytrzymałość na ścinanie badanego połączenia. Badania mikrostrukturalne (SEM oraz TEM) połączone z analizą składu chemicznego wykazały powstanie wydzieleń fazy TiAl3 na granicy rozdziału połączenia. W obszarach fazy TiAl3 obserwowano obecność tlenu. Tworzenie nowych faz na granicy rozdziału połączenie AlTi6/Al2O3 odpowiada za obniżenie wytrzymałości w porównaniu z połączeniem Al/Al2O3. Słowa kluczowe: połączenie AlTi6/Al2O3 joint; wytrzymałość na ścinanie, granica rozdziału Introduction The basis of the technological processes such as soldering, brazing and production of metal matrix composite materials is the assurance of the appropriate wettability of ceramic by liquid metals and receiving the stable joint between the metal and ceramic. Therefore, the wetting of the Al2O3 by liquid aluminium has been investigated by several authors using the sessile drop method [1÷5]. These studies concentrated mainly on the in[...]

Structure and mechanical properties of soldered joints of AZ61 magnesium alloy

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Magnesium and its alloys, possessing excellent properties of extremely low density, high specific strength and good castability, have been widely used in various fields of industry. To broaden out fields of application of magnesium alloys it is necessary to develop filler metals for brazing or soldering magnesium alloys which would enable to obtain satisfactory joint. Conventional methods like welding, brazing, soldering are used for joining magnesium alloys, but these methods run into several difficulties. Magnesium has high affinity with oxygen and the magnesium surface is covered with a thick and very stable oxide film (MgO) which is very difficult to reduce [1]. Low melting temperature and low recrystallization temperature limit the amount of metals that can be used for brazing and soldering. For brazing magnesium alloys filler metals are based on Mg or Zn with the addition of Al, Mn and Zr [2]. Watanabe et al. [3] investigated filler metals for brazing magnesium alloy AZ31B and they developed filler metal composed of In, Mg and Zn with a melting point below 480°C. They also found out that the cross tensile load of the brazed joint decreased as the Zn content in the filler metal increased. Recent investigations made by Liu and Wu [4] showed that there is a possibility of soldering magnesium alloy AZ31B with the filler metal composed of 95% Zn and with the addition of Al, Mn, and Mg at soldering temperature 390°C. There is lack of information about soldering magnesium alloys with higher addition of Al and this paper is focused to investigate filler metals for soldering magnesium alloy AZ61. Experimental procedure The rod of magnesium alloy AZ61 with a diameter of 10 mm was cut into pieces to the length of 10 mm. Each sample consists of two pieces soldered using filler metal based on zinc. There were three compositions of the filler metal: zinc of purity 99.995 wt % (Zn), zinc with 0.15 wt % Cu (ZnCu) and zinc w[...]

Thermodynamic justification for the intermetallic layers formation within the hexagonal single crystal

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Many eutectic systems exhibit either a lamellar or rod-like structure depending on solidification conditions, Elliott [1]. Especially, growth rate plays a crucial role in the lamella/rod transformation. Some impurities also involve the transition, Steen and Hellawell [2]. The impurities change the specific surface free energies and finally modify a mechanical equilibrium at the triple point of the solid/liquid interface. According to the current model assumptions, the mechanical equilibrium varies with solidification conditions (growth rate) and no effect of impurities is observed. A given orientation of crystal manifests a proper growth rate. Some changes of the orientation from an initial state into a final one give also an effect on the lamella/rod transtition, [3]. The theory developed by Jackson and Hunt [4] has tried to predict the threshold rate at which transformation should occur. It yields: a m a m a m a m E P L L R R α α β β α α β β ξ ξ ξ / / / / / / / . + + > + ( ) ( ) (4 )(1 (1 ) ) 1 5 (1) The discerning analysis shows that the above inequality can predict whether an eutectic alloy manifests lamellar or rod-like structure, only. E, P and aj L, aj R - parameters applied in theory [4], j = α, β, ζ = Sβ/Sα, mj - slope of the liquidus lines, respectively, j = α, β. Thus, the inequality characterizes a given phase diagram. Thus, Eq. (1) cannot be applied to describe the structural transformation. It is evident that the Eq. (1) is completely misleading in the case of some predictions connected with structural transformation. Therefore, a new condition for transformation based on the calculation of the minimum entropy production will be applied in the current analysis. All the threshold growth rates will be determined for the (Zn)-Zn16Ti eutectic system by means of the current theorem. According to the current theorem th[...]

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