Diagnosis and Analysis of Oxide Films in Cast Magnesium Alloys by Ultrasonic-Vibration Treatment

Abstract

Magnesium alloys with low density are important light metals, widely used in the aerospace and automotive industries and in the manufacture of communication devices, consumer-electronics appliances and computers products in recent years. However magnesium and magnesium alloys are the most reactive metals so that oxide films easily form on them during the melting or pouring process. These films are difficult to observe by optical micrograph. In this study we propose a simple method to observe oxide films entrapped in cast magnesium alloys. The oxide films are fractured as a result of cavitation erosion on the sample surface that occurs during ultrasonic-vibration treatment. The eroded areas become visible as differently shaped foggy marks. This method of observing and identifying foggy marks is shown to be useful in the diagnosis of oxide films in cast magnesium alloys. In addition, the presented method in the diagnosis of oxide films that formed on magnesium and aluminum alloys are also compared.

Characterization of Oxide Growth on Surface of Al-Mg-Si Welded Joint

“…Consequently, the main oxide entrapped in welded Al alloy is MgO. It was found to be in agreement with Chen and Wei [30] that the main phases of the oxide films are MgO and MgAl 2 O 4 . MgAl 2 O 4 was recorded to have a low free energy so that it is often formed at the interface of the Al matrix and MgO.…”

“…Pure metals and alloys are not stable especially when it has been exposed to a high temperature oxidation environment [28,29]. In the case of welded part, a combination of high temperature and oxidation environment with contaminants resulting from previous welding procedure might lead to the internal degradation at a very rapid rate [30,31]. Porosity defect in fused metal part also increased the penetration of oxygen which in turn acts as a channel that accelerates the oxidation process.…”

The reactive element effect on high-temperature oxidation of magnesium

“…205 The morphology of entrapped oxide in an Mg alloy depends on its chemistry and covers equiaxed, granular, nodular or platelike shapes. 225 The higher aluminium content results in an increase in plate-like shapes at the expense of equiaxed ones, as detected based on an acoustic impedance technique. According to recent findings, the oxide film on molten Mg and Al alloys, when deliberately dispersed using intensive melt shearing, may be used as endogenous particles for effective grain refinement.…”

Inclusions in magnesium and its alloys: a review

“…Chen and Wei 71 proposed an ultrasonic vibration method for the diagnosis of oxide films entrapped in cast Mg alloys. The method is based on the phenomena of acoustic cavitation.…”