Study on hydrogen removal of AZ91 alloys using ultrasonic argon degassing process

• Hydrogen removal of magnesium was first attempted using ultrasonic argon degassing.
• Mechanical properties of the degassed AZ91 alloys are much improved.
• Ultrasonic argon degassing could both remove hydrogen and refine structures.
• The mechanism for ultrasonic argon degassing has been discussed in detail.

Argon degassing, ultrasonic degassing and a novel ultrasonic argon degassing treatment were applied for the hydrogen removal of AZ91 magnesium alloy. The hydrogen concentration, microstructures and mechanical properties have also been investigated. AZ91 alloys contains a high hydrogen concentration. The mechanical properties of the as-cast alloy are much improved using degassing process, which should be mainly attributed to the hydrogen removal. Among the three degassing process, the ultrasonic argon treatment is a high efficient process both for hydrogen removal and microstructure refining. One hand, ultrasonic wave could break up the purged argon bubble to improve the degassing efficiency of these bubbles. On the other hand, ultrasound could also generate many cavitation bubbles in the melt, which should account for the microstructure refinement. The ultrasonic argon treatment involves dynamics between the ascending argon bubbles and ultrasonic effects, such as cavitation and streaming, etc.