Abstract
The effect of ultrasonic temperature on density, microstructure and mechanical properties of vacuum counter-pressure casting ZL114A alloy during solidification was investigated by optical microscopy (OM), scanning electron microscope (SEM) and a tensile test. The results show that compared with the traditional vacuum counter-pressure casting aluminum alloy, the primary phase and eutectic silicon of the alloy with ultrasonic treatment has been greatly refined due to the dendrites broken by ultrasonic vibration. However, the refining effect of ultrasonic treatment on vacuum counter-pressure casting aluminum alloy will be significantly affected by ultrasonic temperature. When the ultrasonic temperature increases from 680 °C to 720 °C, the primary phase is gradually refined, and the morphology of eutectic silicon also changes from coarse needle-like flakes to fine short rods. With a further increase in the ultrasonic temperature, the microstructure will coarse again. The tensile strength and elongation of vacuum counter-pressure casting ZL114A alloy increases first and then decreases with the increase of ultrasonic temperature. The optimal mechanical properties were achieved with tensile strength of 327 MPa and the elongation of 5.57% at ultrasonic temperature of 720 °C, which is 6.3% and 8.2%, respectively, higher than that of alloy without ultrasonic treatment.
Highlights
Aluminum alloys have gained wide applications in the aeronautics and spaceflight industry for their superior comprehensive properties, such as being lightweight, with excellent mechanical performance, good corrosion resistance and castability [1,2,3]
It can be seen from the figure that pouring temperature hashigh, a of vacuum counter-pressure casting aluminum alloy is already very effect on thethe density of in thethe vacuum counter-pressure casting aluminum alloy sample
The course plate-like eutectic silicon that has just nucleated and grown can be crushed by this instantaneous high temperature and high pressure. It can be seen from Equation (1) that the high pressure generated by the collapse of the cavitation bubble will increase with the increase of external pressure, resulting in the cavitation effect and acoustic flow effect of vacuum counter-pressure casting with Ultrasonic treatment (UST) being greatly enhanced under solidification pressure
Summary
Aluminum alloys have gained wide applications in the aeronautics and spaceflight industry for their superior comprehensive properties, such as being lightweight, with excellent mechanical performance, good corrosion resistance and castability [1,2,3]. As an advanced counter-gravity casting technology, the vacuum counter-pressure casting method can ensure that the casting has a good solidification feeding condition, dense microstructure and excellent mechanical property due to its characteristic of filling molds under low pressure and crystallizing under high pressure [6]. Our previous research [5,6,7] indicates that there is an extrusion and infiltration effect that can promote the aluminum alloy molten metal flow toward the dendrite spaces through narrow passages during the solidification process of vacuum-counter pressure casting aluminum alloy. The dendrite will be plastically deformed, even crushed and broken under the extrusion and infiltration effect, which is beneficial to refine the grains and improve the mechanical properties of the aluminum alloy castings.
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