Effects of the grain refiner Mg-Al-C master alloy on the low cycle fatigue life of AZ91D magnesium alloy

摘要

Adding various amounts of Mg-Al-C (Mg:Al:C=l:3:l,in weight ratio) grain refiner in AZ91D as-cast magnesium alloy can not only effectively refine the alloy grain but also substantially enhance the mechanical properties (including low cycle fatigue life). As the addition of Mg-Al-C grain refiner reaches 1.2%(wt), which is the most proper in ratio, the average grain size of the alloy is reduced from the maximum 162μn with no addition of grain refiner to the minimum 57μm, and the alloy can offer the best comprehensive mechanical properties. At the same strain amplitudes, the low cycle fatigue life of the magnesium alloy is proportional to the grain degree refined. When total strain amplitude, Δε_t/2 is 0.2%, the fatigue life of AZ91D + 1.2%Mg-Al-C alloy can reach 13615 cycles , compared with 7694 cycles of AZ91D with no refiner added; when ΔAe_t/2 reaches to 1.2%, the fatigue life of AZ91D alloy is improved from 21 cycles up to 113 cycles after adding 1.2%(wt) Mg-Al-C. Summarily, in the low-cycle fatigue experiments, both the initiation and propagation life of the fatigue crack can be prolonged with the addition of the grain refiner, so the whole fatigue life is increased.