بررسي تاثير عمليات آلتراسونيك بر ساختار و خواص مكانيكي آلياژ منيزيم AZ91

چكيده انگليسي :

Study of the Effect of Ultrasonic Treatment on the Microstructure and Mechanical Properties of AZ91 Magnesium alloy Mohsen Khosro aghayani mohsenmse@ma iut ac ir Date of Submission 2009 06 13 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Behazad Niroumand behzn@cc iut ac irAbstractUltrasonic treatment is an effective but less practiced dynamic nucleation method for grain refinement ofmolten or solidifying alloys In this study the influence of ultrasonic treatment on the microstructural featuresand mechanical properties of AZ91 magnesium alloy was investigated Ultrasonic waves were directed to thesurface of the molten or solidifying alloy using an ultrasonic device with frequency of 20kHz and nominalpower of 600W The parameters investigated included the intensity and duration of ultrasonic treatment aswell as the casting temperature in the mushy zone of the alloy solid fraction before pouring For investigation of the effect of ultrasonic intensity the melt was ultrasonic treated for 5min at 700oC at 0 20 40 and 60 percent of the nominal power of the device and was then poured in a sodium silicate sandmould For study of the effect of time of ultrasonic treatment the melt was ultrasonic treated at 30 of thenominal power of the device for 0 2 and 15min at 700oC and was then poured in a sodium silicate sandmould For investigation of the effect of solid fraction before pouring the alloy was melted and thencontinuously cooled inside the furnace The ultrasonic treatment with 40 of the nominal power of thedevice was started from 605oC i e about 7oC super heat and continued until reaching various temperaturesin the mushy zone of the alloy and then the samples were quenched in water Similar experiments werecarried out with out ultrasonic treatment Cast samples were then cut and their microstructural features andmechanical properties were investigated Size and morphology of Mg dendrites and intermetallic phasessuch as Mg2Si MnFeAl Si and Mg17Al12 were characterized using image analysis techniques Experimental results indicated that with increasing the ultrasonic power or ultrasonic treatment time the sizeof grains and phases decreased while their sphericity increased Tensile strength and elongation of thesamples increased simultaneously with increasing the ultrasonic treatment power or time Results of the continuous cooling experiments indicated that at each casting temperature solid fraction thesize of grains and intermetallic phases decreased and their sphericity increased by ultrasonic treatmentcompared to the conventionally cooled samples Also with increasing the casting temperature within themushy zone under ultrasonic treatment the average length and width of Mg17Al12 either in the quenched zoneor between the primary dendrites decreased At each casting temperature solid fraction the tensile strengthand hardness of the samples increased with ultrasonic treatment while their elongation and impact energyremained almost unchanged Also the results revealed that ultrasonic treatment at higher temperatures lowersolid fractions had a more significant effect on the microstructure and mechanical properties of the castAZ91 alloy Key words Ultrasonic treatment AZ91 magnesium alloy Microstructure Mechanical properties

خسرو آقاياني، محسن

بررسي تاثير عمليات آلتراسونيك بر ساختار و خواص مكانيكي آلياژ منيزيم AZ91

ريز ساختار , روشهاي ديناميكي