【作者】 崔红卫；

【导师】 闵光辉；

【作者基本信息】 山东大学 ， 材料加工工程， 2013， 博士

【摘要】 镁合金具有较高的比强度和比刚度、阻尼减震性好、零件尺寸稳定、机加工性能优良以及可回收性好等优点。因此轻质镁合金已经成为有色金属材料中发展最为迅速的合金系,被誉为21世纪最具发展前途的金属结构材料。与铸造镁合金相比,变形镁合金具有更高的强度、延展性和多样化的力学性能,可以满足作为结构件的要求。准晶增强镁合金由于其良好的综合力学性能而受到国内外工业界的广泛关注。本文采用常规铸造法制备了添加AlTiC中间合金的Mg-Zn-Y镁合金,研究了AITiC中间合金含量对Mg-Zn-Y合金铸态显微组织和力学性能的影响,探讨了AlTiC中间合金的晶粒细化机理以及对准晶相数量、形态等的影响。以均匀化处理后的ZW61合金和ZW61-0.15AlTiC合金为研究对象,研究了不同挤压比、挤压速度对镁合金显微组织、织构和力学性能的影响,对合金的细化机理、断裂行为和强化机制进行了研究,并初步探讨了织构和力学性能之间的关系。对两种综合力学性能良好的挤压态镁合金进行了热处理,探讨了不同热处理工艺(T4、T5和双级时效处理)对镁合金组织和力学性能的影响。研究结果表明,在Mg-Zn-Y合金中加入AlTiC中间合金,既可以细化镁合金组织,又可以增加准晶相I相的数量,添加适量AlTiC中间合金的Mg-Zn-Y合金具有良好的综合力学性能。添加了AlTiC中间合金的铸态Mg-Zn-Y合金经均匀化处理后,第二相的数量明显增多且分布更均匀,其力学性能得到进一步改善。对均匀化处理后的ZW61合金和ZW61-0.15AITiC合金进行挤压,不同的挤压比、不同的挤压速度均可明显导致镁合金的晶粒细化,第二相得到破碎并沿挤压方向分布,大的挤压比将导致晶粒更细小,大小更均匀。挤压后镁合金的拉伸强度、伸长率和冲击韧度均较铸态、均匀化处理态的力学性能有大幅度提高。在小挤压比的条件下进行挤压,两种镁合金的拉伸强度和伸长率与织构强度之间具有较好的对应关系,且伸长率的变化与平均施密特因子m密切相关。在大挤压比条件下进行挤压,两种镁合金的拉伸强度和伸长率与织构强度之间的关系比较复杂,镁合金拉伸强度随挤压速度的变化趋势可以用基面最大极密度的变化趋势来进行表征,而伸长率随挤压速度的变化趋势仍然可以用平均施密特因子m的变化趋势来进行表征。挤压态ZW61合金和ZW61-0.15AlTiC合金在不同温度固溶处理2h,伸长率在350℃较挤压态有明显升高,而在其它温度,拉伸强度和伸长率均较挤压态性能有所降低。在375℃固溶处理不同时间,拉伸强度和伸长率的变化具有类似的趋势,即随着固溶处理时间的延长,先降后升,然后又有所降低。挤压态镁合金经人工时效处理处理后,其力学性能一般有所降低。两种挤压镁合金经双级时效处理后力学性能均有所降低,但未经固溶处理,直接进行双级时效处理后的综合力学性能有明显提高。更多还原

【Abstract】 Magnesium and magnesium alloy are becoming more and more attractive for many engineering structural applications owing to their low density and high specific strength. However, the application of most magnesium alloys has been greatly restricted due to their poor strength, oxidation and creep resistance. In order to extend the application of magnesium alloys, many methods have been reported to improve mechanical properties.Icosahedral quasicrystalline phase (Ⅰ-phase) that has attractive mechanical and physical properties attributed to their unique atomic structure, such as high strength, high hardness at elevated temperature and low friction coefficient has been reported in many alloy systems. Recently, it has been reported that the Mg-Zn-Y alloys containing Ⅰ-phase as a secondary solidification phase exhibit good mechanical properties at room temperature and elevated temperature, which provide a good method for the development and application of new magnesium alloys.In this paper, several Mg-Zn-Y alloys with different contents of AlTiC master alloys were fabricated by using the conventional casting method. The effect of the AlTiC master alloy contents on as-cast microstructure and mechanical properties was studied. The grain refinemnt mechanism of the AlTiC master alloy and its effect on amounts and morphology of quasicrystals were also discussed. Based on the as-homogenized ZW61alloy and ZW61-0.15AlTiC alloy, the influence of different extrusion ratio and extrusion speed on the microstructure, texture and mechanical properties was investigated, and the refinement mechanism, fracture behavior and strengthening mechanism were studied. Two as-extruded magnesium alloys with good comprehensive mechanical properties were heat treated, and the effect of different heat treatment processes (T4, T5and double-step ageing treatment) on microstructure and mechanical properties was discussed.The results showed that the addition of AlTiC master into Mg-Zn-Y alloy not only could refine the microstructure, but also could increase the amounts of the Ⅰ-phase. Mg-Zn-Y alloy with proper AlTiC master alloy had good comprehensive mechanical properties. After the as-cast Mg-Zn-Y alloys with AlTiC master alloys were homogenized, the amounts of the second phases increased obviously and distributed more uniformly and the mechanical properties were further improved.Different extrusion ratios and different extrusion speeds could cause the as-homogenized ZW61alloy and ZW61-0.15AlTiC alloy grain refinement and the second phases were broken and mainly distributed along the direction of extrusion. The ultimate tensile strength (UTS), elongation and impact toughness of the as-extruded magnesium alloys were increased remarkably compared with the as-cast and as-homogenized ones.There was a good relationship between UTS, elongation of the two magnesium alloys and the intensity of basal PF with the small extrusion ratio, and the change of elongation was most associated with the average Schmid factors m. Extruded at large extrusion ratio, the relationship between UTS, elongation and the intensity of basal PF was complicated. The tendency of UTS of the two alloys with different extrusion speeds could be represented by maximum intensity of basal PF. And the tendency of elongation was still associated with the average Schmid factors m.As-extruded magnesium alloys were solid solution treated at different temperature for2h, the elongation increased obviously at350℃. However, the UTS and elongation decreased a little at other temperature. Solid solution treated at375℃for different time, the changes of the UTS and elongation had the similar tendancy, that is, with the increase of time, the properties decreased first and then increasd, and further decreased.In general, the mechanical properties of ZW61alloy and ZW61-0.15AlTiC alloy are lower than the as-extruded after artificial ageing treatment.The mechanical properties of the two alloys decreased after double-step ageing treatment. However, the comprehensive mechanical properties increased remarkably after direct double-step ageing treatment without solid solution treatment.更多还原