Mg-gd (y) The Heat-resistant Magnesium Alloy Material And Heat Treatment Study

The poor mechanical properties of magnesium alloys at hightemperatures severely limit their applications. The Mg-Gd-Y systemalloys have better mechanical properties and creep-resistance at elevatedtemperatures than other magnesium alloys. In this paper, Mn and Scelements were introduced into the existing Mg-Gd-Y system alloys tofurther improve their microstructures and mechanical properties atelevated temperatures. OM, SEM, TEM, ICP and tensile test were used tostudy the rnicrostructures, mechanical properties, fracture behavior,plastic deformation behavior and processing parameters of theMg-Gd-Y-based alloys with different compositions.The evolution of microstructures and mechanical properties duringheat-treatment of the binary Mg-Gd and the terary Mg-Gd-Y alloys arestudied. The Solidification microstructures of these alloys are made up ofandβphase. Mg₅Gd and Mg₂₄Y₅ constitute theβphase in thebinary alloy, while their continuous solid-solution theβphase in theterary alloy. The strength of Mg-Gd binary alloys increases and theplasticity decreases with increase of Gd content. The properties ofMg-Gd-Y ternary alloys are better than those of Mg-Gd binary alloys,which indicates that combination of Gd and Y alloying is more beneficialthan only Gd addition.The effects of solution time on the microstructures ofMg-5Gd-1Mn-0.3Sc and Mg-5Y-Mn-Sc alloys were investigated. Theresults showed that the solidification microstructures ofMg-5Gd-1Mn-0.3Sc exhibited coarse dendrite structure and a lot ofsecond phases existed in the dendrite regions or on the grain boundaries.Quite a bit GdMg3, formed during non-equilibrium solidification, can notbe eliminated by solution heat-treatment. The solidificationmicrostructure of Mg-5Y-Mn-Sc is much coarser, with coarse grains andunder development dendrite, large numbers of twin grains appearing"plait" shape and the alignment of second phase particles. The changesof grain size behaved abnormally during solution treatments at 520℃for different time. The gains evolve from large to the small and then to thecoarse. Time and temperature of solution treatment can be controlled,refining grains of the studied alloy can be obtained accordingly.The effects of Mn or Sc, and heat treatment on the microstructuresand mechanical properties of the terary Mg-Gd-Y alloy have beeninvestigated. The grain microstructures of the studied alloy with Mn arenot different from those of the terary Mg-Gd-Y alloy. The phase structurein the alloy with Mn develops: the complicated rich-Mn phases exist inthe cast structure, which are some compounds from Mn metal and rareearth metals. Grain-refining of Mn in the terary Mg-Gd-Y alloy does nottake place. Sc reduces the solubility of rare earth elements in themagnesium matrix alloy, which leads to increasing of the elongation anddecreasing of the strength of the Mg-9Gd-4Y-0.6Mn-0.3Sc alloy. Theexperiment results indicate that the optimal solution temperature forMg-9Gd-4Y-0.6Mn and Mg-9Gd-4Y-0.6Mn-0.3Sc alloys is 525℃.The extruding can improve the structures and properties of the alloys,Only is the extruding temperature higher than 400℃, can the rods besuccessfully extruded under the conventional conditions. The dynamicrecrystallization was finally developed and the recrystallized equiaxedcrystal grains occurred in the Mg-9Gd-4Y-0.6Mn andMg-gGd-4Y-0.6Mn-0.3Sc alloys during extruding at various temperatures.The average size of grains becomes smaller with decrease of extrudingtemperature. After the studied alloys are extruded at 450℃, the very finegrains about 15μm can be obtained. The grain-refining of the extrudedalloys containing manganese is obvious as compared to the previouscoarse grains of the as-cast alloy. The tensile testing shows that themechanical properties of the Mg-9Gd-4Y-0.6Mn alloy at lowtemperature, room temperature and high temperature have greatlyexceeded those of WE54 and WE43, which are thought to be goodheat-resistant magnesium alloys. So the Mg-9Gd-4Y-0.6Mn alloy is thepotentially-developing beneficial and heat-resistant ones. The ultimatetensile strength of the Mg-9Gd-4Y-0.6Mn alloy reaches a high quality of210MPa while tensile testing at 300℃, which exhibits superplaslicalbehavior while tensile testing at 350℃However, the Mg-9Gd-4Y-0.6Mn-0.3Sc alloy exhibits superplaslical behavior whentensile testing is performed at 300℃. The ability of deformation, grainrefining and heat-resistant properties of the Mg-9Gd-4Y alloy areimproved by alloying with additional element Mn. The ageing behaviorof Mg-9Gd-4Y-0.6Mn-0.3Sc alloy is affected by additional element Sc,which ageing temperature is different obviously from it that the alloycontaining Mn.