MICROSTRUCTURES AND PROPERTIES OF RECIPROCATINGLY EXTRUDED Mg-6.4Zn-1.IY ALLOYS

An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn-Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1 Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1 Y alloy consists of the a-Mg solid solution, icosahedral Mg3 YZn6 quasicrystal, and Mg3 Y2Zn3 and MgZn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Y2 Zn3 and MgZn2 phases dissolved into the matrix, whereas, Mg3YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.     

Microstructre of Mg-6.4Zn-1.1Y Alloy Fabricatec by Rapid Solidification and Reciprocating Extrusion

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1Y magnesium alloy with thickness of 50-60冚m were obtained by a melt spinning single-roller device, and then the flakes were processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in 冄-Mg solute solution, and impede the formation of Mg3Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the -Mg solid solution and icosahedral Mg3YZn6 quasicrystal. Dense rods can be made from the flakes by 2-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3YZn6 compounds are precipitated and distributed uniformly, whereas the rods possesses fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: 冄-magnesium solid solution as matrix and fine icosahedral Mg3YZn6 quasicrystal which disperses uniformly in the matrix.     

MICROSTRUCTURE OF Mg-6.4Zn-1.1Y ALLOY FABRICATED BY RAPID SOLIDIFICATION AND RECIPROCATING EXTRUSION

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60 um were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in a-Mg solute solution, and impede the formation of Mg3 Y2 Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The mierostrueture of the flakes consists of the a-Mg solid solution and icosahedral Mg3 YZn6 quasierystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: amagnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.     

高强Mg-Gd-Y-Zn-Zr合金的微观组织和力学性能

通过金属模铸、热挤压和时效处理(T5)工艺过程制备出高强Mg-7Gd-4Y-1.6Zn-0.5Zr合金,并利用光学显微镜、XRD、SEM及TEM分析研究Mg合金不同状态下的显微组织和力学性能。结果表明:Mg-7Gd-4Y-1.6Zn-0.5Zr合金的铸态组织主要由α-Mg基体和沿晶界分布的片层状第二相Mg12Zn(Gd,Y)组成,经过热挤压变形后,合金晶粒显著细化,时效处理过程中Mg12Zn(Gd,Y)相上析出少量细小的颗粒状Mg3Zn3(Gd,Y)2相。时效态合金的抗拉强度、屈服强度和伸长率分别达到446 MPa、399 MPa和6.1%,其强化方式主要为细晶强化和第二相强化。     

铸造冷却速度对Mg-4.4Zn-0.3Zr-0.4Y挤压态合金组织性能的影响

本文通过两种不同冷却速度制备成分相同、铸造组织特征不同的Mg-4.4Zn-0.3Zr-0.4Y铸态合金,研究不同铸造组织特征对挤压变形态合金组织和力学性能的影响。研究结果表明：与空冷铸造合金相比较,通过水冷冷却增大了熔体冷却速度,使铸态组织得到细化,抑制了W-相（Mg3Y2Zn3相）的形核,并促进了I-相（Mg3YZn6相）的生成,获得了更大体积分数的准晶相(I-相)。经过挤压变形后,水冷铸造合金中的再结晶晶粒细小均匀,经过挤压变形破碎的细小I-相颗粒弥散分布在基体上,{0002}基面织构得到弱化,而{101 ?2}织构强度增强,从而使挤压态Mg-4.4Zn-0.3Zr-0.4Y合金的强度和塑性都得到了大幅的提高。水冷铸造Mg-4.4Zn-0.3Zr-0.4Y合金经过挤压变形后,屈服强度和抗拉强度分别达到297.0MPa和327.3MPa,与空冷铸造挤压态合金相比分别提高了46.4MPa和21.4MPa。水冷铸造Mg-4.4Zn-0.3Zr-0.4Y挤压态合金的延伸率达到14.8%,与空冷铸造挤压态合金相比增大了4.7%。     

往复挤压对Mg-0.85Zn-0.15Y-0.6Zr铸态组织和力学性能的影响

研究了往复挤压对准晶增强Mg-0.85Zn-0.15Y-0.6Zr铸态合金显微组织及力学性能的影响。结果表明,往复挤压可大幅度细化Mg-0.85Zn-0.15Y-0.6Zr铸态合金组织,且使I相等相对均匀地分布在α-Mg基体中。同铸态合金相比,挤压后Mg-0.85Zn-0.15Y-0.6Zr合金的屈服强度、抗拉强度和延伸率分别提高了75.8%,43.2%和35%。     

Effect of hot extrusion on microstructure and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy

The microstructure and mechanical properties of as-cast and as-extruded Mg-Zn-Y alloy （Mg-11 %Zn- 0.9%Y, mass fraction） containing Mg3 YZn6 quasicrystal were studied. The eutectic icosahedral quasicrystal phase （I-phase） is broken and almost distributes along the extrusion direction, and fine I-phase with nano-size is precipitated during the extrusion. The a-Mg matrix grains are refined due to recrystallization occuring during the hot extrusion. Some {1012} twins are observed in the extruded ZW1101 alloy. And {0002}（1010） fiber texture is formed in matrix alloys after hot extrusion. The extruded alloy exhibits high strength in combination with large elongation at room temperature. The strengthening mechanism of the as-extruded alloy was discussed.     

稀土Y元素对铸态镁合金组织与力学性能的影响

采用熔炼工艺制备了Mg-2.0Zn-0.2Ca与Mg-2.0Zn-0.2Ca-2Y合金,研究了两种合金的铸态组织及力学性能。结果表明,Y元素的添加细化了Mg-2.0Zn-0.2C合金的铸态组织。Mg-2.0Zn-0.2Ca合金主要由α-Mg与少量Mg₇Zn₃相组成,添加2wt%的Y后,改变了Zn在Mg基体中的固溶度,降低了其固溶强化效果,同时组织中形成了I相和W相。添加Y元素后,合金的规定塑性延伸强度升高,从41.0 MPa升高到50.6 MPa;伸长率降低,从12.6%降低到4.0%。     

往复挤压对Mg-6%Si合金组织与力学性能的影响

研究了往复挤压对铸造Mg-6%Si (质量分数,下同)合金微观组织和力学性能的影响。结果表明：往复挤压4道次后,Mg-6%Si合金的显微组织得到显著细化,粗大树枝状的初生Mg2Si相变为细小颗粒状,而汉字状的共晶Mg2Si相也变为弥散分布的点状相,且这些颗粒状的Mg2Si相均匀分布在基体中。往复挤压4道次后,Mg-6%Si合金的抗拉强度和延伸率分别提高了82.3%和810.9%。断口分析表明,往复挤压合金的断裂模式由脆性断裂转变为韧-脆性断裂。     

热处理对铸态Mg-4.2Zn-1.5RE-0.7Zr镁合金显微组织和力学性能的影响

研究热处理工艺对铸态Mg-4.2Zn-1.5RE-0.7Zr镁合金显微组织和力学性能的影响。结果表明：铸态Mg-4.2Zn-1.5RE-0.7Zr镁合金的显微组织主要由α-Mg、T相和Mg51Zn20相组成;单级等温时效（325°C,10 h）以及双级时效（325°C,4 h）＋（175°C,14 h）处理均未能使T相和Mg51Zn20相溶入基体,且晶粒也未明显长大。在325°C下时效10 h,晶内析出大量短杆状β′1相,延长时效时间将导致β′1相粗化及数量减少。Mg-4.2Zn-1.5RE-0.7Zr镁合金在325°C下时效10 h后具有最高的屈服强度（153.9 MPa）和抗拉强度（247.0 MPa）,相比铸态合金分别增加48 MPa和23 MPa,伸长率降低至15.6%。Mg-4.2Zn-1.5RE-0.7Zr合金经双级时效（325°C,4 h）＋（175°C,14 h）处理后的屈服强度和抗拉强度与单级等温时效处理（325°C,10 h）的相当,但伸长率有所下降。此外,不同状态下Mg-Zn-RE-Zr镁合金的断裂主要表现为准解理断裂,但局部特征有差别。     

Zn与Mg质量比对热挤压Al-Zn-Mg-Sc显微组织及力学性能的影响

制备了Al-2Mg-0.4Sc、Al-5Mg-0.4Sc、Al-5Mg-2Zn-0.4Sc和Al-5Zn-2Mg-0.4Sc等4种合金并在350℃进行热挤压,通过光学显微镜(OM),X射线衍射(XRD),扫描电子显微镜(SEM)、室温拉伸测试,研究了Zn/Mg比对于Al-Zn-Mg-Sc合金组织与力学性能的影响。结果表明,Zn/Mg比的提高对于铸态晶粒具有细化作用,挤压后发生动态再结晶,晶粒尺寸显著减小,但挤压态晶粒尺寸并未随Zn/Mg比的提高而减小。另一方面,Zn/Mg比的提高使Mg32(Al,Zn)49第二相数量增加,且呈现更明显的网状结构。挤压态Al-Zn-Mg-Sc合金屈服强度随Zn/Mg比的提高而提升,主要由于大量Al3Sc粒子与碎化的第二相呈网状分布于晶界,使第二相强化起到主导作用。     

不同Y含量对ZM21镁合金组织和力学性能的影响

本文主要通过OM、SEM、EDS和XRD等研究了铸态及挤压态Mg-2Zn-1Mn-xY (Y=0,0.8,2.2,wt.%) 镁合金显微组织和力学性能。由实验结果可知,稀土Y的添加,不仅可以细化铸态及挤压态合金晶粒,还可以弱化挤压态合金的基面织构强度,从而同时提高合金的强度以及韧性。本文中最优化合金挤压态Mg-2Zn-1Mn-xY合金具有良好的力学性能,与原始Mg-2Zn-1Mn合金相比,屈服强度从164MPa提高到204MPa、抗拉强度从237MPa提高到298MPa以及延伸率从12%增加到18%。     

Zn对铸态Mg-10Gd-3Sm-0.5Zr合金组织和力学性能的影响

采用熔炼铸造法制备了添加0~2%Zn(质量分数)的Mg-10Gd-3Sm-0.5Zr合金,通过X射线衍射、扫描电镜和拉伸性能测试等分析了Zn对铸态Mg-10Gd-3Sm-0.5Zr合金组织与性能的影响。结果表明:铸态Mg-10Gd-3Sm-0.5Zr合金由粗大枝晶α-Mg基体和晶界处半连续分布稀土相Mg41(Sm,Gd)5和Mg5Gd(Sm)组成,加入Zn元素后,在合金中产生了新相(Mg,Zn)3(Sm,Gd)1;铸态Mg-10Gd-3Sm-xZn-0.5Zr合金室温拉伸力学性能随着Zn元素含量的增加先升高后降低,当Zn的添加量为1%时,综合力学性能最好,其抗拉强度、屈服强度、伸长率分别为215 MPa、173 MPa和5.5%;合金的断裂方式主要为脆性断裂,加入Zn元素后有向韧性断裂转变的趋势。     

Microstructure and mechanical properties of extruded Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy

The Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy ingot and sheet were prepared by casting and hot extrusion techniques,and the microstructure,age hardening behavior and mechanical properties were investigated.The results show that the as-cast alloy mainly containsα-Mg solid solution and compounds of Mg5RE and Mg24RE5(RE=Gd,Y and Nd)phases.The grain size is refined after hot extrusion,and the Mg5RE and Mg24RE5 compounds are broken during the extrusion process.The extruded alloy exhibits remarkable age hardening response and excellent mechanical properties in the peak-aging state.The ultimate tensile strength,yield strength and elongation are 310 MPa,201 MPa and 5.8%at room temperature,and 173 MPa,133 MPa and 25.0%at 300℃,respectively.     

Mg-1Mn-1Zn镁合金的组织与腐蚀行为研究

采用金属型铸造制备Mg-1Mn-1Zn(wt％)三元合金,并将其挤压成棒材.利用光学显微镜、扫描电子显微镜、浸泡试验法等研究了Mg-1Mn-Zn合金的微观组织及其在0.9％NaCl溶液中的腐蚀行为.结果表明,Mg-1Mn-1Zn合金室温组织由树枝状的α-Mg相、非平衡共晶MgZn化合物相和脱溶析出的α-Mn相构成.热挤压使等轴晶粒沿挤压方向被拉长,呈现纤维状组织.Mg-1Mn-1Zn合金的平均腐蚀速率随时间增加逐渐降低.经过264 h浸泡后,挤压态Mg-1Mn-1Zn合金的平均腐蚀速率为0.44 mm/a,比铸态合金的低26.7％.     

Microstructures and mechanical properties of the extruded Mg-4Y-2Gd-xZn-0.4Zr alloys

Microstructures and mechanical properties of the Mg-4Y-2Gd-0.4Zr alloy with Zn additions have been investigated. The investigation suggests that the mechanical properties of the alloys have been greatly improved after hot extrusion due to the refinement of microstructures, especially the elongations. The extruded Mg-4Y-2Gd-1.0Zn-0.4Zr alloy displays excellent tensile properties. The ultimate tensile strength and the yield tensile strength are 291 and 228 MPa, respectively, with an elongation of 28%. The additions of Zn have an obvious effect on refining microstructure of the extruded alloys, and the vicker hardness increases with increasing Zn additions. The age hardening responses of the extruded alloys have been investigated at 220 °C. These alloys display unobvious ageing hardness responses.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

Mg-6Gd-3Y-2Zn-0.5Zr镁合金的组织和性能

设计了新型Mg-6Gd-3Y-2Zn-0.5Zr镁合金,并用光学显微镜、扫描电镜及拉伸试验机对合金铸态、均匀化态及挤压态的显微组织特征和力学性能进行了研究。结果表明,铸态Mg-6Gd-3Y-2Zn-0.5Zr合金组织主要由α-Mg基体和沿晶界分布的块状长周期堆垛有序结构相组成,均匀化处理(450℃×16h)促使细小层片状的长周期堆垛有序结构相由晶界向晶内生长。挤压态Mg-6Gd-3Y-2Zn-0.5Zr合金在200℃下时效处理,无明显时效硬化现象,但挤压态合金具有优良的强韧性能,室温抗拉强度、屈服强度和伸长率分别为335MPa、276MPa和17%。     

二次挤压对MB26镁合金棒材组织及性能的影响

采用二次挤压工艺制备MB26(Mg-6.3Zn-0.7Zr-0.9Y-0.3Nd)镁合金棒材,研究不同挤压比对MB26合金组织性能的影响,通过金相(OM)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等手段分析稀土元素在合金中的分布及其对微观组织的影响。结果表明:合金在二次挤压过程中发生动态再结晶,随着挤压比的增加,再结晶晶粒细化,当挤压比λ=25时,平均晶粒尺寸为1.9μm,合金力学性能达到最优;合金经挤压变形后出现大量W(Mg3Y2Zn3)相和β′(MgZn)相,均呈弥散分布,钉扎晶界,阻碍了动态再结晶晶粒的长大。通过数据拟合得到该合金屈服强度与晶粒尺寸的Hall-Petch关系。     

挤压态和时效态Mg-Zn-Mn-Sn-Y合金的组织性能

利用光学显微镜、X射线衍射和扫描电镜等对挤压态和时效态Mg-6Zn-1Mn-4Sn和Mg-6Zn-1Mn-4Sn-0.5Y镁合金的微观组织和力学性能进行研究。结果表明：与ZMT614镁合金相比,添加Y元素后,ZMT614-0.5Y晶粒得到细化,综合力学性能得到提高。Mg-6Zn-1Mn-4Sn-0.5Y合金的相组成为α-Mg、Mg Zn2、Mn、Mg2Sn和MgS n Y相。经过T6热处理后,合金的抗拉强度和屈服强度明显得到提高,伸长率明显被降低。理论计算表明,在挤压态合金中,细晶强化和固溶强化产生重要的作用,而在T6热处理态合金中,析出强化产生决定作用。