The effect of Ce addition (up to 3%) and extrusion ratio on the microstructure and tensile properties of ZK60 Mg alloy

In this study, attempts have been made to investigate the effects of both Ce addition and Extrusion Ratio (ER) on the microstructure and tensile properties of ZK60 alloy. With this aim, different amounts (1, 2 and 3 wt%) of Ce were added to a based ZK60 alloy and then the investigated alloys experienced the hot extrusion process with different ERs (12:1 and 18:1). It was found out that Ce addition could refine the cast (non-deformed) microstructure as the finest grain size (35 mu m) was obtained in Ce-containing (3 wt%) alloy. Besides, the results of XRD demonstrated that, in addition to Mg7Zn3 that already existed in the base alloy, a new precipitate (MgZn2Ce) would form in the presence of Ce. This led to an increase in fraction of the precipitates with Ce addition. Microstructural observations showed that applying the extrusion process on the cast alloys, especially with higher ER, would significantly refine the size of grains and precipitates. The grain refinement might be due to the microstructural evolutions taken place during exerting the extrusion forces as well as the dynamic recrystallization. It was found out that Ce addition in both cast and deformed conditions could enhance the hardness and strength of the alloys, while it would have no or negative effect on their elongation. Compared to the cast condition, extruded alloys exhibited far better mechanical properties, especially when higher ER (18:1) has been employed; as the highest hardness (88 HV), yield (308 MPa) and tensile strengths (354 MPa) have been obtained in 3 wt% Ce-containing alloy extruded with ER of 18:1. However, higher ER resulted in lower elongation of the studied alloys.