Application of Ultrasonics on Preparation of Magnesium Alloys

This chapter mainly describes the application of ultrasonic on preparation of magnesium alloys, which includes all of the interesting and novel research results of authors in the past decade. The chapter includes the following topics to readers: the ultrasonic cavitation behavior in magnesium alloys; the effect of ultrasonic treatment on melt structure; ultrasonic degassing of magnesium alloys; effect of ultrasonic melt treatment on microstructure of magnesium alloys; dual-frequency ultrasonic treatment on solidification of magnesium alloys; and ultrasonic direct-chill (DC) casting process of magnesium alloys billets, including the novel variable-frequency ultrasonic technology. The chapter almost covers all the aspects of ultrasonic application on preparation of magnesium alloys and can help readers have a systematic understanding of ultrasonic melt treatment on magnesium alloys

Effects of varied ultrasonic semi-continuous casting on microstructure and mechanical properties of ZK60 magnesium alloy

A varied ultrasonic technology was applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60(Mg-Zn-Zr) alloy with φ255mm in semi-continuous casting, which was analyzed comparatively with those of ones without ultrasonic treatment and static frequency ultrasonic semi-continuous casting. The change of acoustic pressure via time in two acoustic field was simulated by numerical method. The varied-frequency acoustic field can promote the formation of small α-Mg globular grains and change the distribution and morphology of β phases in the castings, greatly refining grain size in the alloy compared with that of static frequency field. Ultimate tensile strength and elongation of the alloy with varied-frequency field are increased to 280 MPa and 8.9%, respectively, which are 19.1% and 78.7% higher than those of ones obtained from billet without ultrasonic treatment and are 11.6% and 28.2% higher than that of ones by static-frequency ultrasound treated billets. Different refinement efficiencies appear in different regions of billet, which is attributed to the sound attenuation. The varied-frequency ultrasound can improve refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects

Liquid structure of aluminum binary alloys characterized by electrical parameters under electromagnetic field

The electrical parameters of aluminum binary alloys (Al–Fe and Al–Si alloys) have been investigated in the presence of alternating current (AC) and direct current (DC) electromagnetic fields. The results show that both thermoelectric power and electrical resistivity of Al–Fe alloys increase in the AC/DC electromagnetic field, which indicates that the liquid structure is changed by the electromagnetic treatment. Study on Al–Fe alloys with different Fe content reveals that Al-1.99wt.% Fe alloy shows the sharp increase of transient variation Δ S ( S : thermoelectric power) and inflection of residual variation Δ S _0 at near eutectic composition in AC electromagnetic field, which is comparable with the electrical resistivity in DC electromagnetic field. In addition, the effects of electromagnetic parameters (setting current, frequency and duty cycle) on voltage/current waveform of power system and thermoelectric power have been further studied. After comparing the results of voltage and current waveforms, it shows that the output current can be regarded as a better evaluation index to the effects of electromagnetic parameters on the thermoelectric power. This quantitative method can clearly analyze the effects of electromagnetic parameters on the liquid structure, which is characterized by the thermoelectric power

Discharge performance of Mg–Al–Cd anode for Mg-air Battery

This work investigated the discharge properties of the Mg-6Al-xCd alloy as a potential anode material for the Mg–air battery. The influence of the Mg-6Al-xCd alloy with cadmium content ranging between 0.5% and 1% on the electrochemical and discharge performances was investigated by means of microstructure characterization, electrochemical performance measurement and discharge test of the alloys. The results show that Mg-6Al-1.0Cd has the highest anode efficiency and specific capacity of 41.38% and 993.54 mAh/g, respectively. This good discharge performance is attributed to the addition of cadmium, which can inhibit self-corrosion and reduce the galvanic corrosion of the magnesium anode. The Mg-6Al-1.0Cd alloy can be used as a potentially ideal material for the Mg–air battery anode

Effects of Nd/Gd value on the microstructures and mechanical properties of Mg–Gd–Y–Nd–Zr alloys

Four Mg–Gd–Y–Nd–Zr alloys were prepared by mold casting to investigate the effects of Nd/Gd ratios on microstructures and mechanical properties. The as-cast alloys mainly consist of α-Mg and β-Mg5(GdYNd). Volume fractions of the second phase increase and grains were slightly refined with the rising Nd/Gd ratio, when the alloying addition is equal. Meanwhile, fibers of second phase also increase in the extruded alloys when the Nd/Gd value increases. However, the Nd/Gd ratio could hardly influence the mechanical properties of the extruded alloys. The aging hardening response of the extruded alloy differs due to different Nd/Gd ratios. The potential mechanisms have also been discussed in detail

The grain refinement of Mg alloy subjected to dual-frequency ultrasonic melt treatment: A physical and numerical simulation

Ultrasonic melt processing of magnesium (Mg) alloys has received widespread attention. However, the cavitation behavior and microstructure evolution are difficult to be directly observed in high temperature melts. In this work, single-frequency ultrasonic field (SUF) and dual-frequency ultrasonic field (DUF) were introduced into succinonitrile (SCN) melt and real-time images of dendrite growth and evolution were captured to explore the regulation mechanism of DUF on melt solidification structure. Numerical simulation and corresponding experiments were performed to investigate the acoustic pressure distribution and cavitation area of DUF in Mg alloy melt. Ultrasonic treatment increased the SCN dendrite growth rate and refined the solidification microstructure, and a higher efficiency was achieved by DUF when compared to SUF when the total electric power was the same. DUF decreased sound pressure attenuation and enlarged cavitation area. A result of this improvement was that its grain refinement efficiency was 13.8% and 25.6% higher than SUF at 15 kHz and 20 kHz, respectively. The input power ratio plays a crucial part in improving the grain refinement efficiency of DUF. While ensuring the symmetrical distribution of cavitation area, the grain refinement efficiency can be significantly optimized by appropriately increasing the power share of 15 kHz ultrasound is optimal at a power ratio of 2:1

Experimental Analysis and Mathematical Modeling on Mg-Li Alloy Sheets with Three Crystal Structures during Cold Rolling and Heat Treatment

The microstructural evolution, mechanical properties, and mathematical relationship of an α, α + β, and β phase Mg-Li alloy during the cold rolling and annealing process were investigated. The results showed that the increased Li element gradually transformed the Mg matrix structure from hcp to bcc. Simultaneously, the alloy plasticity was improved remarkably during cold rolling. In the annealing process, a sort of abnormal grain growth was found in Mg-11Li-3Al-2Zn-0.2Y, but was not detected in Mg-5Li-3Al-2Zn-0.2Y and Mg-8Li-3Al-2Zn-0.2Y. Moreover, the mechanical properties of alloy were evidently improved through a kind of solid solution in the β matrix. To accurately quantify this strengthening effect, the method of mathematical modeling was used to determine the relationship between strength and multiple factors

Effect of Zn/Y atomic ratio on precipitation behavior and dynamic recrystallization behavior of Mg–Zn–Y alloy under different extrusion temperature

Precipitation behavior and dynamic recrystallization (DRX) behavior of Mg–Zn–Y alloys with different Zn/Y atomic ratios under different extrsuion temperatures were systematically investigated in this work. The results shows that the types of precipitated phases in the casted alloys are changed with the increase of Zn/Y atomic ratio. After extrsuion, the brittle W-phases in Mg98.7Zn1Y0.3 and Mg98Zn1Y1 alloys are broken into finer particles along the extrusion direction, but the resistance of W-phases to grain growth is weak at higher extrusion temperature. However, Mg97.5Zn1Y1.5 alloy exhibits relatively stable grain size at different extrusion temperatures, due to the significant inhibitory effect of LPSO phases on grain growth at high temperatures. The banded LPSO phases with wide phase spacing can promote DRX behavior via particle stimulated nucleation (PSN) resulting in highest DRX fraction. Nevertheless, the lamellar LPSO phases could effectively hinder the grain boundary migration and dislocation motion, which is against the nucleation and growth of DRX grains. It is precisely due to the influence of LSPO phases on the DRX behavior and its own kinking effect that Mg97.5Zn1Y1.5 alloy has better heat resistance. Mg97.5Zn1Y1.5 alloy exhibits excellent tensile strength and ductility, with ultimate tensile strength (UTS) of 413 MPa, yield strength (YS) of 330 MPa and elongation (EL) of 12.1% after extrusion at 573 K. The good ductility is mainly due to the coordinated deformation ability of the LPSO phase and the activated non-basal slip effect. The synergistic effect of lamellar LPSO phase and kinking deformation effectively refines the microstructure of the alloy and improves the strength