CAJ | 학술논문

研究不同Zn含量的Mg-x%Zn-1%Mn(x=4, 5, 6, 7, 8, 9) 变形镁合金经热机械处理后的显微组织和力学性能的演变.在热挤压过程中,显微组织经动态再结晶得以充分细化.随着Zn含量的增加,动态再结晶晶粒有长大的趋势,然而,随之增加的第二相流线阻碍其长大.固溶处理使动态再结晶晶粒快速长大,但高Zn含量会阻碍晶界迁移,从而使最终的晶粒较为细小.在单级时效过程中,与基体共格的MgZn2弥散相会从过饱和固溶体中析出;在双级时效时,预时效过程中析出的大量纳米尺度的GP区为第二级时效过程中MgZn2相的析出提供了有效的异质形核核心,从而使该强化相的弥散度增加.挤压态试样的力学性能对Zn含量的变化不敏感,抗拉强度在300-320 MPa之间波动,伸长率在11%-14%之间波动.时效态试样的强度随着Zn含量的增加以抛物线形式增加,单级时效态试样的抗拉强度从278 MPa增加到374 MPa,而双级时效态试样的抗拉强度从284 MPa增加到378 MPa,但所有试样的伸长率都小于8%.当Zn含量超过其在Mg-Zn二元合金体系中的最大固溶度(约6.2%)后,合金的强度增加缓慢但伸长率却迅速降低.因此,含6%Zn的Mg-Zn-Mn合金具有最佳的力学性能,即经过单级和双级时效后,合金的抗拉强度分别为352 MPa和366 MPa, 伸长率分别为8%和5%.
연구불동Zn함량적Mg-x%Zn-1%Mn(x=4, 5, 6, 7, 8, 9) 변형미합금경열궤계처리후적현미조직화역학성능적연변.재열제압과정중,현미조직경동태재결정득이충분세화.수착Zn함량적증가,동태재결정정립유장대적추세,연이,수지증가적제이상류선조애기장대.고용처리사동태재결정정립쾌속장대,단고Zn함량회조애정계천이,종이사최종적정립교위세소.재단급시효과정중,여기체공격적MgZn2미산상회종과포화고용체중석출;재쌍급시효시,예시효과정중석출적대량납미척도적GP구위제이급시효과정중MgZn2상적석출제공료유효적이질형핵핵심,종이사해강화상적미산도증가.제압태시양적역학성능대Zn함량적변화불민감,항랍강도재300-320 MPa지간파동,신장솔재11%-14%지간파동.시효태시양적강도수착Zn함량적증가이포물선형식증가,단급시효태시양적항랍강도종278 MPa증가도374 MPa,이쌍급시효태시양적항랍강도종284 MPa증가도378 MPa,단소유시양적신장솔도소우8%.당Zn함량초과기재Mg-Zn이원합금체계중적최대고용도(약6.2%)후,합금적강도증가완만단신장솔각신속강저.인차,함6%Zn적Mg-Zn-Mn합금구유최가적역학성능,즉경과단급화쌍급시효후,합금적항랍강도분별위352 MPa화366 MPa, 신장솔분별위8%화5%.
The roles of Zn content and thermo-mechanical treatment in affecting microstructures and mechanical properties of Mg-x%Zn-1%Mn (mass fraction, x=4, 5, 6, 7, 8, 9) wrought Mg alloys were investigated. The microstructure was extremely refined by dynamic recrystallization (DRC) during extrusion. With increasing Zn content, the DRC grains tended to grow up, at the same time, more second phase streamlines would be present, which restricted the further growing. During solution treatment, the DRC grains would rapidly grow up; however, higher Zn content could hinder the grain boundary expanding, which results in finer ultimate grains. MgZn2 dispersoid particles which are coherent with the matrix would precipitate from the supersaturated solid solution during the one-step aging process, and nano-sized GP zones formed during the pre-aging stage of the two-step aging provide a huge amount of effective nuclei for the MgZn2 phases formed in the second stage, which makes the MgZn2 particles much finer and more dispersed. The mechanical properties of as-extruded samples were not so sensitive to the variation of Zn content, the tensile strength fluctuates between 300 and 320 MPa, and the elongation maintains a high value between 11% and 14%. The strength of aged samples rises as a parabolic curve with increasing Zn content, specifically, the tensile strength of one-step aged samples rises from 278 to 374 MPa, and that of two-step aged ones rises from 284 to 378 MPa, yet the elongation of all aged samples is below 8%. When Zn content exceeds its solid solution limit in Mg-Zn system (6.2%, mass fraction), the strength rises slowly but the elongation deteriorates sharply, so a Mg-Zn-Mn alloy with 6% Zn possesses the best mechanical properties, that is, the tensile strengths after one- and two-step aging are 352 and 366 MPa, respectively, and the corresponding elongations are 7.98% and 5.2%, respectively.