Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

Abstract

High zinc content Mg-Zn-Al alloys have the potential to be used as high pressure die casting (HPDC) alloys for applications up to 150 C. However, these alloys show high tendency to hot tearing and microporosity. Rheo-diecasting (RDC) is an innovative semisolid HPDC process, which can effectively eliminate the formation of primary magnesium dendrites and convert them into fine, globular particles. This very positive change in the morphology and distribution of the primary phase reduces the subsequent formation of various casting defects. In this study, a composition of Mg-10Zn-4.5Al was selected from the Mg-Zn-Al system and processed with both HPDC and RDC. It is shown that, samples produced by the RDC process exhibit substantially reduced hot cracks, few gas pores, and a nearly uniform distribution of fine, globular primary particles. These microstructural changes resulted in much improved strength and elongation, which are comparable to those of AZ91D, while the processing temperature is much lower. It is concluded that high zinc content Mg-Zn-Al alloys have good potential to be exploited as commercially useful alloys by the RDC process.

Improved mechanical properties in vacuum-assist high-pressure die casting of AZ91D alloy

“…It could be seen that the sample in conventional HPDC process exhibited the worst mechanical properties, while the best occurred in the improved vacuum-assist HPDC process, i.e., ∼20% higher ultra tensile strength, double elongation and treble low-cycle fatigue life. Similar to the studies by Liu et al (2005), Tzamtzis et al (2010) and Ji et al (2005Ji et al ( , 2013, the best mechanical properties as well as the flattest fracture morphology could be attributed to the uniform microstructure and reduction of porosity, which in turn were resulted from a lower EVP and less amount of ESCs achieved in the HPDC.…”

“…Liu et al (2005), Tzamtzis et al (2010) and Ji et al (2005Ji et al ( , 2013 reported that the improved mechanical properties in the melt-conditioning HPDC and rheo-die casting could be attributed to the fine uniform microstructure and elimination of large gas porosity as a consequence of solidification under high shear rate. Niu et al (2000), Patel et al (2012), Wen et al (2012) and Wan et al (2013) studied the vacuum-assist HPDC process, and suggested that the improved mechanical properties could be attributed to the reduction of gas pores.…”

Microstructure and Tensile Properties of the Mg-6Zn-4Al-xSn Die Cast Magnesium Alloy

“…The Mg-Zn-Al (ZA) series alloys are put forward as cost-effective and creep-resistant alloys to narrow the gap between AZ91D and some creep-resistant but expensive alloys [7]. However, the mechanical properties of the Mg-Zn-Al alloys still need to be enhanced.…”

Influence of Sc on Microstructure and Mechanical Properties of High Zn-Containing Mg Alloy

“…Most research works involved with Mg-Zn-RE (rare earth) alloy system are focused on low Zn content (<6 wt%) system and Mg-Zn-Y alloy is the most representative one [1][2][3][4]. High Zn content alloys have low production temperatures and good flowability, but relevant research is not comprehensive and most works are focused on the Mg-Al-Zn alloy system [5][6][7].…”