EFFECT OF HEAT TREATMENT ON HIGH CYCLE FATIGUE PROPERTIES OF Mg-4Y-3Nd-1.5Al ALLOY

The effect of different heat treatment conditions on high cycle fatigue properties of newly developed Mg-4Y-3Nd- 1.5Al alloy was studied. The results show that the minimum fatigue strength of the as-cast alloys is 66 MPa. The fatigue strength of the alloys after solution treatment (525 degrees C x 6 h + 550 degrees C x 12 h) is 77 MPa, and the fatigue strength is increased by about 17%. After peak aging treatment (525 degrees C x 6 h + 550 degrees C x 12 h + 200 degrees C x 20 h), the fatigue strength of alloys is increased to 95 MPa, which improves approximately 43% on the basement of the as-cast alloys 66 MPa. The fatigue performance of the alloys is closely correlated with the microstructure of the alloys. There are plenty of thick reticular Mg5RE eutectic phases at the grain boundary of the as-cast alloys. With the lowest fatigue strength, cracks can easily form at the eutectic phases. After solution treatment, the reticular phase of the alloy dissolves, the plasticity and deformability of the alloy are enhanced, the process of crack initiation is delayed, and the fatigue strength of the alloy is improved. Abundant nanoscale fi00 phases precipitate in the matrix of the aged alloy, improving the strength of the matrix, giving the ability to hinder the deformation of the matrix, delaying crack formation delayed, and greatly improving the fatigue performance.