Study On The Microstructure And Performance Of Mg-4Y-3Nd Alloy After Aging Treatment

Magnesium alloy become the modern alternative to steel, aluminum alloy andplastics so as to realize the ideal of lightweight materials because of its qualitativelight, high specific strength, good vibration performance and has been widely used intransportation,“3C”products and aerospace field. But due to the high temperaturecreep performance is poor, restricting its development and application scope. Sostrengthening and the strengthening mechanism of the magnesium alloy become animportant direction in the research of magnesium. Adding the rare element hasbecome the most common method to impore its high temporature performance andthermal creep and the WE series alloy containing yttrium and neodymium elements isthe most wildly used in heat resistant magnesium alloy like WE43and WE54whichcould regular work for a long time at250℃and keep performance for1000h at300℃and has been applied on the plane and the car engine cylinder. T6treatment isthe most commonly used reinforcement method, but so far its aging strengtheningmechanism is still not too clear, so this topic through high temporature agingtreatment research precipitation regularity of precipitated phase at different agingstages and the phase transformation.The board Mg-4Y-3Nd alloy was prepared by metal mold casting method andthen hot extrusion processing. After solution aging treatment, studied themicrostructure at different aging stages, the second phase preperation rule, the phasestructrue and aging hardening by optical microscope, X-ray diffractometer(XRD),scanning eletron microscope(SEM) and energy spectrometer(SEM-EDS) and Vickers.The results showed that: the second phase preferrential nucleated in the grainboundary in intracrytalline directon, with the increase of aging time, the second phasestarted to precipitate continuous in the intracrytalline and the second phase distributedhomogeneously in the matrix without the serial dendrite of as-cast alloy. In theprocess of aging, the precipitated phase were fine at the beginning, then grown up a little and after aging4h the volume gradually grew up until aging32h the largen wereobvious. The phase structure study showed that: T6Mg-4Y-3Nd alloy is composed ofα-Mg solid solution, Mg24Y5, Mg2Y, Mg41Nd5and Mg14Nd2Y. With formation ofprecipitates, lattice parameters of α-Mg solid solution change considerably, thediffraction angle2-theta of a certain crystallographic plane decrease, correspondinginterplanar of a certain crystallographic planes increase.The aging hardness curve showed that: there existed three aging harding peaks inthe0.5-32h aging process, including a disappeared quickly small peak at0.5h and twoobvious peaks at4h and24h. Every aging harding peak indicated phase shift betweenprecipitates. There mainly were β″phase that could only exist with a short time of0.5h aging alloy with the phenomenon of hardness decreasing of1h aging alloy andthen β″phase gradually translated to β′phase with a peak at4h and then β′phasegradually translated to β1phase with a peak at24h and then β1phase graduallytranslated to β phase. There were β′, β1, β phase coexistence phenomenon in8to32haging.