Research On Low-Cycle Fatigue Behavior Of Die Casting Mg-Al-Mn(-RE) Magnesium Alloy

Magnesium alloy is a kind of light metal materials of very suitable for casting, die casting magnesium alloy mainly has the advantages of good quality, high production efficiency, low processing cost, it is currently one of the research hotspots in materials. Fatigue fracture is one of the most main failure form of a material, therefore, research of die casting magnesium alloy of low cycle fatigue behavior has a certain practical value. In this investigation, according to the different processing condition of Mg-Al-Mn-Gd alloy and Mg-Al-Mn-Ce alloy are invested on the low cycle fatigue behavior of magnesium alloys, so as to provide a reliable basis for fatigue resistance theory.In this paper, through microstructural observation results of die casting magnesium alloys show: die casting Mg-Al-Mn-Gd magnesium alloy texture become grain refinement after ageing, and the smaller Mg₁₇Al₁₂ phase at the grain boundary precipitate a lot, while in the crystal Mg₃Gd phase precipitation. Treatment of die casting Mg-Al-Mn-Ce magnes- ium alloy also has precipitationed the second phase along the grain boundary.The results of low-cycle fatigue tests revesl that the different processing states of Mg-Al-Mn-Gd and Mg-Al-Mn-Ce alloys exhibit the cyclic strain hardening. On the die casting Mg-Al-Mn-Gd magnesium alloy, the same applied total strain amplitudes, aging state alloy exhibited higher fatigue life than die casting alloy, but with the degree of hardening about the total strain amplitude and processing state of alloy; Aging treatment can enhance the cyclic stress amplitude at the lower total strain amplitudes(△ε_t/2≤0.5%) during whole fatigue deformation of the die casting Mg-Al-Mn-Gd magnesium alloy; Aging treatment on die casting Mg-Al-Mn-Gd magnesium alloys can not enhance the cyclic stress amplitude, will even lower the cyclic stress amplitude at the higher total strain amplitudes(△ε_t/2≥0.6%); On the die casting Mg-Al-Mn-Ce magnesium alloy, the same applied total strain amplitudes, aging state alloy exhibited lower fatigue life than die casting alloy; For the Mg-Al-Mn-Gd and Mg-Al-Mn-Ce alloys with different treatment states, the relations between elastic strain amplitude, plastic strain amplitude and fatigue fracture loads reverse cycle can be described by Basquin and Coffin-Manson equations, respectively, in addition, a linear relationship between cyclic stress amplitude and plastic strain amplitude is also noted for them; The observations on fracture surface of fatigued specimens reveal that for the Mg-Al-Mn-Gd and Mg-Al-Mn-Ce alloys with different treatment states, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly in the total strain controlled fatigue loading conditions.