Effects Of Heat Treatment On Microstructures And Properties Of Mg-4Zn-xNd-0.5Zr Alloys

Magnesium alloys is one of the most lightweight metallic materials in engineeringapplications now, which have such virtues as high specific stiffness and specific strength,good heat dispersing performances, good damping capacity and electromagneticinterference resistance properties, steady accessory size as well as recycling potential, andhave been found a wide application in aeronautical and automotive industries. The widelyused Mg-Zn-Zr series alloys have been producted by extrusion technics, such as ZK60,which have high intensity and tenacity, but theirs ductility is poor than Mg-Al series alloys.Thus, we are study and develop a new magnesium alloy with rare earth elements in orderto improve Mg-Zn-Zr series alloys,intensity and tenacity. The microstructures, mechanicalproperties and fracture behaviors for extruded Mg-4Zn-0.5Zr alloys containing0.5%,1.0%and1.5%Nd after T5and T6heat treatments were investigated. And the influence of heattreatment on both microstructure and mechanical property of the alloy is determined.The microstructure shows that the grain size reduces according to the order of T6treated, extruded and T5treated states.The results of tensile experiments show that with increasing the Nd content, theultimate tensile strength, yield strength and elongation to fracture of the Mg-4Zn-xNd-0.5Zr alloys with different processed states firstly increase and then decrease, wherethe alloys with the Nd content of1.0%exhibit better comprehensive performance.Although the T6treatment leads to a decrease in the tensile properties of the extrudedMg-4Zn-xNd-0.5Zr alloys, the T5treatment can effectively improve the tensile propertiesof the alloys.The results of low-cyclic fatigue tests show that during fatigue deformation, theextruded Mg-4Zn-xNd-0.5Zr alloys exhibit the cyclic strain hardening, softening and stablecyclic stress response, which mainly depends on the imposed total strain amplitude and thecontent of rare-earth-element Nd. When the content of Nd is1.0%, alloys with T5treatmenthave the highest cyclic stress levels than other alloys. For three alloys with different Nd content, the relationship between the plastic strain amplitudes and reversals to failureexhibits a single slope linear behavior.The fractographic results reveal that under tensile loading conditions, the extrudedMg-4Zn-xNd-0.5Zr alloys after T5treatment show typical ductile fracture characteristics,while the alloys after T6treatment show mixed fracture include cleavage planes anddimples. while under low-cycle fatigue loading conditions, the extruded Mg-4Zn-xNd-0.5Zr alloys after T5treatment show that the fatigue cracks initiate and propagatetransgranularly from the surface of fatigue samples.