| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 101 === Various thermomechanial treatments are conducted to strengthen the extremely light LZ141 and LAZ1110 magnesium alloys. The strengthened alloys are investigated by microstructural observation, XRD analysis, microvickers hardness, impact and tensile tests. Experimental results indicate both hardness and tensile strength of hot-rolled (HR) alloys increase after cold rolling (CR), but decrease after solid-solution treatment (SS). The SS process has no strengthening effect. For SS + CR80% specimens, the maxium tensile strength is 176.4MPa which is tensiled in the direction perpendicular to the rolling direction. The impact test of HR 141 alloy shows the highest impact value is 0.51J/mm2 which occurs at the notch direction perpendicular to the rolling direction. The impact value is 0.4 J/mm2 at -196oC and is not sensitive with the testing temperature. The tensile curves of HR LZ141 alloy have obviously Portevin-Le Chatelier (PLC) effect. The strengthening mechanism of LAZ1110 alloy with little Be and Sc (LAZ1110BS) is also investigated and compared to that of LAZ1110 alloy which had studied in this group two years ago. The best method to strengthen LAZ1110BS is solid-soluted in air furnace, water quenched and then cold-rolled 80%, which can reach the tensile strength of 280MPa, i.e., specific tensile strength of 189.2. As the same time, LAZ1110BS thermomechanical-treated by SS+CR80% can retard the degradation of the hardness when specimens are aged at room temperature for long time. The hardness of LAZ1110 ribbons prepared by rapid solidification process has the handness of 111.3Hv, which is much higher than bulk LAZ1110 alloy which has the harndess of 58.1Hv.
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