The Effect of Rapid Deformation Process to Improve Creep and Tensile Resistance of AZ۹۱ Magnesium Alloy Plates

Demand for increasing strength to weight ratio, elimination of electromagnetic waves, and vibration damping has led to the wide application of magnesium-base alloys such as AZ۹۱ in various industries like aerospace, military, vehicle, and shipbuilding. However, because of the unstable secondary particles and casting defects located on the rough grain boundaries and in the dendritic regions, due to sliding of the grain boundary, the creep resistance and tensile strength of Mg alloys at high temperatures reduce. To improve the high-temperature properties, rapid deformation processes such as friction stir processing can be employed. In this study, the influence of multi-pass friction stir processing on microhardness, tensile, and creep behavior of AZ۹۱ at several temperatures from ۲۵ to ۲۱۰ °C has been studied. Optical microscopy and scanning electron micrograph were used to study the microstructure of the cast and processed samples and Clemex commercial software was used for grain size measurement. The experimental results indicated that at room temperature, the microhardness, tensile, and creep strength of the processed samples as compared to the unprocessed ones increased by ۲۳, ۲۹ and ۳۸%, respectively. In addition, after multi-pass friction stir processing, the tensile and creep strength of the samples at ۲۱۰ °C  increased by ۳۱ and ۴۷%, respectively. Also, the average grain size of the multi-passed friction stir processed AZ۹۱ alloy decreased by ۸۸%. The maximum ultimate tensile strength of ۲۷۶ MPa was obtained at the tool rotational speed of ۱۲۰۰ r/min, the traverse speed of ۶۰ mm/min, and the tool tilt angle of ۳°. The empirical results indicated that this rapid deformation process can be useful in enhancing the mechanical properties of AZ۹۱ alloy at high temperatures.

Keywords:

Rapid Deformation Process , Multi-Pass Friction Stir Processing , tensile strength , Creep , AZ۹۱ Alloy