| Magnesium alloy has low density,high specific strength,good damping and shock absorption performance.At the same time,it has low heat capacity,high speed of solidification,the good performance of casting forming and other excellent characteristics.The magnesium alloy also has easy to recycle,and it has been well known as the prospective green engineering structure materials in the 21 st century.The commercial magnesium alloy always exist some shortcomings which will affect the properties of the magnesium alloy,so using the heat treatment can effectively reduce the defect.This paper main study the microstructure,fatigue property and fatigue crack propagation rate of the ZK60 magnesium alloy.It has profound influence on application in production and daily life.Through the universal testing machine,the as-rolled metal and the heat treated samples of properties of tensile properties were studied.The ZK60 magnesium alloy's fatigue life and crack growth rate was measured by SDS-100 fatigue machine.Through SEM and XRD,we can analysis the magnesium alloy and particles.The grain size of as-rolled ZK60 magnesium alloy is 26?m,and the average grain size of the specimen by the solution heat treatment is about 31?m.With the aging time from five hours to twenty hours,the grain size is reduced and then becomes bigger.At the 10 hours,the grain size becomes minimum(10?m).The tensile strength of the as-rolled ZK60 magnesium alloy is 294 MPa and the tensile strength of the specimen by the solution treatment is 301 MPa.After the aging treatment,the tensile strength of the sample is 325 MPa.The tensile strength of the sample is greatly improved with respect to the as-rolled ZK60 magnesium alloy,and the elongation and yield strength of the specimen are improved.Through the fatigue test,when the number of cycles is 107,the fatigue strength of the specimen is 91.62 MPa and the fatigue strength of the specimen by the solution treatment and solution aging treatment is 102.46 MPa and 117.76 MPa,respectively.So,after the aging treatment,the fatigue strength of the specimen is about 28.31% higher than as-rolled ZK60 magnesium alloy.The sample of the asrolled ZK60 magnesium alloy which is brittle fracture.By observing the fracture surface of specimen by the heat treatment,the fracture surface is quasi-cleavage fracture in the crack initiation.The fatigue crack propagation experiment show that the fatigue crack propagation rate of the specimen at aging time at 5 hours is slightly slower than specimen by the solution treatment.At the aging time of 10 hours,the property of resistance fatigue crack propagation is improved.When the aging time is 15 hours,the crack propagation rate doesn't continue to decrease.When the aging time is 20 hours,the crack propagation rate of the sample is accelerated.At the aging time is 10 hours,the crack resistance of the specimen is optimized.The SEM examinations revealed that the surface features of cracks.In the initial region,the solution-treated alloy contains many pits,and it is the brittle fracture.The aged alloy has a relatively-bright tearing edge.We find the secondary cracks on the surface in the aged specimen during the stable crack growth region.During the last region,the aged specimen show dimples,which could enhance the fatigue crack propagation resistance.The crack tip of the sample's plastic radius can be calculated by the plastic radius formula.Therefore,plastic radius of specimen by solution heat-treatment and aging treatment are 10.5?m and 10.1?m.They have smaller plastic radius than grain size and aging specimen has a smaller plastic zone so that the specimen has better property of resistance fatigue propagation. |
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