Effect Of Deep Cryogenic Treatment On Microstructure And Mechanical Properties Of Extruded ZK60 Magnesium Alloy

In this paper,ZK60 magnesium alloy was used in the study.ZK60 magnesium alloy extruded rods with different extrusion parameters were obtained by hot extrusion of ZK60 magnesium alloy,and deep cryogenic treatment and aging treatment were carried out.The effects of cryogenic treatment on the mechanical properties and microstructure of extruded ZK60 magnesium alloy under different extrusion conditions were studied.The microstructure and mechanical properties of extruded ZK60 magnesium alloy after deep cryogenic treatment were studied.The extruded ZK60 magnesium alloy with an extrusion ratio of 15 and an extrusion temperature of 300?and 400?was subjected to deep cryogenic treatment,and two peaks appeared in hardness,and the hardness reached a maximum at the second peak point.Both the strength and the elongation of the two have increased,but the increase is not large.After deep cryogenic treatment,the second phase precipitates from the grain boundaries and grains.The extruded ZK60 magnesium alloy with extrusion temperature of 400?is more fully dynamic recrystallization,and the grain refinement is easier.The second phase is precipitated.More,deep cryogenic treatment works better.The extruded rodZK60 magnesium alloy with extrusion temperature of400?and extrusion ratio of 30 is deep cryogenically treated.The hardness value also shows a double-peak law with the extension of deep cryogenic treatment time,and is squeezed with ZK60 magnesium alloy with extrusion ratio of 15.Compared with the pressure bar,the strength and plasticity increase more,the grain is refined,and the bulk second phase at the grain boundary breaks into fine second phase particles,which are dispersed on the grain boundary and inside the grain.After the aging treatment of the extruded ZK60 magnesium alloy with the extrusion temperature of 400?and the extrusion ratio of 30,the hardness increased first and then decreased.After 12 hours of aging treatment,the hardness value reached the peak value.Compared with the deep cryogenic treatment,only one peak hardness value appears during the aging treatment,and the peak hardness value is lower than the second peak hardness value occurring during the deep cryogenic treatment.The strength and plasticity increase during the aging treatment is also smaller.The extruded ZK60 magnesium alloy with extrusion temperature of 400?and extrusion ratio of 30 is subjected to aging treatment and deep cryogenic treatment,and some second phase precipitates.The second phase is mainly MgZn and MgZn₂;after aging treatment,the microstructure The morphology of the second phase in the interior is mainly long rods or strips,and after cryogenic treatment,the morphology of the second phase in the tissue is mainly fine dots.The grain refinement and the dispersion distribution of a large number of point-like second phase particles have a comprehensive effect on the performance of the extruded ZK60 magnesium alloy.The strength and plasticity of the extruded ZK60 magnesium alloy after 12 hours of deep cryogenic treatment were significantly improved,in which the tensile strength was increased by 18 MPa,the yield strength was increased by 8 MPa,and the elongation was increased by 4.5%.The grains are refined,the precipitation of the second phase particles is increased,the size is reduced,and the dispersion is distributed at the grain boundaries and inside the grains.