Zn-Al Eutectic Alloy Research Articles

Local mechanical properties and plasticity mechanisms in a Zn-Al eutectic alloy

In multiphase alloys, the mechanical properties are controlled by both the local properties of individual microstructural constituents, as well as the mutual effect of these constituents as an aggregate. To this end, we systematically studied the local mechanical properties and deformation mechanisms of the microstructural constituents in a ZnAl4Cu1Mg0.31 alloy using nanoindentation tests at room temperature (25 °C) and 85 °C. The obtained strain rate sensitivity and activation volume suggest dislocation-dominated deformation in the primary η-Zn phase and grain/phase boundary sliding in the eutectoid structures.Further, the strain partitioning between individual microstructural constituents and their roles on macroscopic deformation at 85 °C was investigated using quasi in-situ digital image correlation (DIC), supplemented with non-rigid image registration. The DIC measurements showed that eutectic and eutectoid colonies carry higher strain than the primary η-Zn phase grains. The presented approaches and results can therefore be used to design new Zn-Al alloys and also other multiphase alloys with improved mechanical properties.

Dependence of microstructural, mechanical and electrical properties on growth rates in directional solidified Zn—Al—Bi eutectic alloy

Zn—5%Al—0.2%Bi (mass fraction) alloy was directionally solidified upward at a constant temperature gradient with a wide range of growth rates using a Bridgman-type directional solidification furnace. The eutectic spacings, microhardness, ultimate tensile strength and electrical resistivity for directionally solidified Zn—Al—Bi alloy were measured. Dependence of eutectic spacings, microhardness, ultimate tensile strength and electrical resistivity on growth rates was obtained by linear regression analysis. The results obtained in the present work for low growth rates (smaller than 450.0 μm/s) are in good agreement with experimental results obtained in previous work for directional solidified Zn—Al eutectic alloy with a similar growth rate but differs from the Jackson—Hunt eutectic theory and those obtained in previous experimental works at higher growth rates. The critical growth rate might be 450.0 μm/s for the Zn—Al—Bi eutectic alloy. From the plot of heat flow versus temperature, enthalpy of fusion, specific heat difference between liquid and solid phases and melting temperature for the Zn—Al—Bi alloy are found to be 112.55 J/g, 0.291 J/(g·K) and 660.20 K, respectively.

Effect of Cu Addition to Zn-12Al Alloy on Thermal Properties and Wettability on Cu and Al Substrates

Abstract The thermal properties, electrical resistivity, thermal linear expansion and tensile strength of a new high-temperature lead-free solder based on a eutectic Zn-Al alloy with 0.5, 1.0, or 1.5 at. pct Cu added were studied. Wettability studies on Cu substrate were performed with flux at 773 K (500 °C) for 60, 180, 240, 900, 1800, and 3600 seconds, and for 480 seconds at 733 K, 753 K, 773 K, 793 K, and 823 K (460 °C, 480 °C, 500 °C, 520 °C, and 550 °C, respectively). The experiment was designed to demonstrate the effect of the addition of Cu on the kinetics of the formation and growth of the CuZn, Cu5Zn8, CuZn4, and Al4Cu9 phases, which were identified by X-ray diffraction analysis. Wetting tests were also performed on the Al substrate, for 15 and 30 seconds at 773 K and 793 K (500 °C and 520 °C, respectively). Very low contact angles on Al pads were obtained. The electrical resistivity of Zn-Al-Cu alloys was slightly higher than that of the ZnAl eutectic alloy. The present results are discussed with respect to the available literature on Zn-Al and Zn-Al-Cu alloys.

Wetting of Cu and Al by Sn-Zn and Zn-Al Eutectic Alloys

Wetting properties of Sn-Zn and Zn-Al alloys on Cu and Al substrates were studied. Spreading tests were carried out for 3 min, in air and under protective atmosphere of nitrogen, with the use of fluxes. In the case of Zn-Al eutectic, spreading tests were carried out at 460, 480, 500, and 520 °C, and in the case of Sn-Zn eutectic at 250, 300, 350, 400, 450, and 500 °C, respectively. Solidified solder/substrate couples were cross-sectioned and subjected to microstructure examination. The spreading tests indicated that the wetting properties of eutectic Sn-Zn alloys, on copper pads do not depend on temperature (up to 400 °C), but in the lack of protective atmosphere, the solder does not wet the pads. Wettability studies of Zn-Al eutectic on aluminum and copper substrates have shown a negative effect of the protective nitrogen atmosphere on the wetting properties, especially for the copper pads. Furthermore, it was noted that with increasing temperature the solder wettability is improved. In addition, densities of liquid solders were studied by means of dilatometric technique.

Thermal Properties and Wetting Behavior of High Temperature Zn-Al-In Solders

Solders for ultrahigh-temperature applications were defined by Vianco as those able to sustain working conditions with temperatures as high as 573 K, with momentary temperature rise up to 623 K. Zn-Al eutectic alloy (12 at.% Al) fits such defined criteria with respect to its melting temperature. It was found that small additions of indium to Zn-Al eutectic lower its melting temperature. The aim of this work is to assess if and to what extent thermal properties and wetting behavior are affected. It was found that addition of In increases electrical resistivity and coefficient of thermal expansion value. Wetting angles on Cu and Al substrates of liquid Zn-Al eutectic-based alloys containing up to 1.5 at.% of In were studied with the sessile drop method, after wetting at 773 K in the presence of flux. A decrease of apparent wetting angle was observed with increasing concentration of In. After wetting tests solidified alloy-substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis.

Directional solidification and physical properties measurements of the zinc-aluminum eutectic alloy

Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32–250.0 μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus. The values of eutectic spacing were measured from transverse sections of the samples. The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V−0.53 and ΔT=0.0245V0.53, respectively. The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature. Microhardness of directionally solidified samples was also measured by using a microhardness test device. The dependency of the microhardness on growth rate is found as Hv=115.64V0.13. Afterwards, the electrical resistivity (r) of the casting alloy changes from 40×10−9 to 108×10−9 Ω·m with the temperature rising in the range of 300–630 K. The enthalpy of fusion (ΔH) and specific heat (Cp) for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/(g·K), respectively by means of differential scanning calorimetry (DSC) from heating trace during the transformation from liquid to solid.

Interfacial structure and formation mechanism in ultrasonically aided liquid bonding of Al18B4O33/Al composites in air

Alumina borate whisker reinforced aluminium metal matrix composites were liquid bonded in air. The liquid filler metal of a Zn–Al eutectic alloy could get into the clearance between composites couples by the action of ultrasonic capillarity. The bond/composite interface was eroded, so that a rough interface formed and the oxide film could be removed completely under the action of ultrasonic vibration for 3 s. The shear strength of the bond increases with ultrasonic time. A removal model for the oxide film on the composites during ultrasonic aided liquid bonding was established.

Capillary filling process during ultrasonically brazing of aluminium matrix composites

Alumina borate whisker reinforced aluminium metal matrix composites were ultrasonically brazed in air. The liquid filler metal (FM) of a Zn–Al eutectic alloy could get into the clearance between composite couples by the action of ultrasonic capillarity. The velocity of the FM getting into the clearance decreases with increasing clearance width. The time exhausted to remove completely the oxide film on the surface increases with increasing clearance width. The oxide film could be removed completely and the metallurgical bonding formed under the action of ultrasonic vibration for sufficient time. The shear strength of the bond could reach up to 145 MPa (the nominal strength of the Zn–Al filler alloy).

Phase boundary sliding model controlled by diffusionsolution zone in superplastic deformation

With scanning electron microscope (SEM), the surface morphology of phase boundary sliding (PBS) in superplastic deformation (SPD) of Zn-Al alloy and the diffusion behavior of Zn, Al interfaces in their powers’ sintering have been investigated. The results show that Zn-Al eutectoid microstructure can be achieved through their powders’ sintering, and the diffusion characteristic between Zn and Al is just a demonstration of Kirkendall effect, in which Zn can dissolve into Al whereas A1 can hardly dissolve into Zn. During sintering, a diffusion-solution zone α′ has formed and subsequently transformed into a eutectoid microstructure in the cooling process. The superplastic deformation mechanism of Zn-Al eutectic alloy is phase boundary sliding which is controlled by the diffusion-solution zone α′. If the diffusion-solution zone α′ is unsaturated, it will have much more crystal defects and the combination between α′ and phase β is weak, thus the process of phase boundary sliding becomes easily; on the contrary, if the diffusion-solution zone α′ becomes thick and saturated, the sliding will be difficult.

Interaction of Al-Si, Al-Ge, and Zn-Al eutectic alloys with SiC/Al discontinuously reinforced metal matrix composites

Interactions between Al-Si, Al-Ge, and Zn-Al eutectic alloys with SiC whisker-reinforced aluminium metal matrix composites were studied as a function of temperature above the eutectic melting temperature. Penetration extended several millimetres into the composite for the Al-Si and Al-Ge alloys but was restricted to a thin surface layer (50 μm) for the Zn-Al alloy. The extent of the penetration zone for the aluminium alloys containing silicon and germanium was also affected by the thermal-mechanical treatment of the composite: limited penetration was observed for hot-pressed material whereas extensive penetration was observed for mechanically worked material. Mechanisms for the observed phenomena are discussed in terms of the wettability of the SiC whiskers by the eutectic alloys, the formation of channels during mechanical working as well as the fine grain size of the composite.

一方向凝固したZn-Al共晶合金の減衰能

一方向凝固したZn-Al共晶合金の減衰能