Grain refinement of AZ31 magnesium alloy by AI-Ti-C-Y master ahoy

Al-Ti-C-Y master alloy was prepared by combining SHS technique and melting-casting method. The microstructure of master alloy and its grain-refining effect on AZ31 alloy were investigated by means of OM, XRD, SEM and EDS. Experimental results indicated that the prepared master alloy consisted of α-Al, TiAl3, TiC and Al3Y phases, and exhibited good grain-refining performance of AZ31 alloy. Morphology of α-Mg changed from coarse dendritic to free equiaxed and the average grain size of α-Mg matrix reduced from the original 580 to 170 μm after adding 1.0 wt.% master alloy. The grain refining efficiency of Al-Ti-C-Y master alloy on AZ31 alloy was mainly attributed to heterogeneous nucleation of TiC particles and grain growth restriction of Al-Y compound or TiC at grain boundaries.     

细晶Mg-Al-Ti-C中间合金的制备及其对AZ91D组织和性能的影响

采用两步法+铜模喷铸的方式制备具有颗粒增强和细晶强化作用的Mg-Al-Ti-C中间合金,并研究了其对AZ91D组织和性能的影响。通过OM、SEM、XRD、硬度及拉伸试验对中间合金和AZ91D的组织形貌和力学性能进行分析。结果表明,两步法制备得到了Mg-Al-Ti-C中间合金,经过铜模喷铸后,TiC颗粒尺寸大幅度减小,且弥散分布于Mg-Al-Ti-C中间合金中;用该细晶Mg-Al-Ti-C中间合金处理AZ91D,后者的抗拉强度提高了19.8%,硬度提高了64.9%;TiC颗粒既有颗粒增强作用,也能作为AZ91D凝固时的异质形核核心,起到细晶强化作用。     

Effect of Y Addition on Microstructure and Constituent Phases of Al-Ti-C Master Alloy

Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0%Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.     

Influence of neodymium on high cycle fatigue behavior of die cast AZ91D magnesium alloy

High cycle fatigue behavior of die cast AZ91D magnesium alloy with different Nd contents was investigated.Axial mechanical fatigue tests were conducted at the stress ratio R=0.1 and the fatigue strength was evaluated using up-to-down load method on specimens of AZ91D with different Nd contents.The results showed that the grain of AZ91D alloy was refined,the size and amount of β-Mg17Al12 phase decreased and distributed uniformly with increasing Nd content.At the number of cycles to failure,Nf=107,the fatigue...     

稀土Nd对AZ 31镁合金铸态组织和力学性能的影响

利用气氛电阻炉制备了AZ 31-xNd合金(x=0.05%,0.1%,0.2%,0.4%,0.6%),采用光学显微镜(OM)、扫描电子显微镜(SEM)和电子能谱分析仪(EDS)对不同Nd含量的实验合金进行了显微组织观察和分析,结果发现,Nd在AZ 31-xNd合金中形成了Al_3Nd和Mg_(12)Nd相,这些含Nd相导致AZ 31镁合金在凝固过程中的晶粒细化,从而提高了AZ 31镁合金的铸态室温力学性能,随着Nd含量的增加,合金的铸态室温抗拉强度极限和延伸率均先升高后降低.     

Effects of precipitates on grain size and mechanical properties of AZ31-x% Nd magnesium alloy

The effects of precipitates on grain size and mechanical properties of as-cast AZ3 1-x%Nd magnesium alloy were investi- gated, and the affecting mechanism was also discussed. The results indicated that Al2Nd phase, AlllNd3 phase and a few AI-Mn-Nd-Fe phase were furmed when adding 0.38 wt.%-1.46 wt.% Nd into AZ31 melt, coarse AI2Nd transformed into Al11Nd3 gradually with the increasing of Nd content. Due to structure and size transformation and content increasing of AI-Nd phase, the grain size of AZ31-x% Nd alloy increased firstly, and then decreased with the increment of Nd content. After reaching a minimum value, once again it rose up, provided that Nd content was further increased. The tensile property reached its optimal value when the adding amount of Nd content was 1.05 wl.%, however, adding excessive amount of Nd deteriorated both ultimate strength and elongation ofAZ31 alloy.     

双螺旋搅拌法制浆工艺参数对AZ91D合金半固态组织的影响

双螺旋搅拌工艺制备了AZ91D合金半固态浆料,获得金属半固态加工要求的细小、等轴分布均匀的非枝晶组织。研究了熔体温度、搅拌速度和剪切时间对该组织的影响规律。结果表明:采用合适的搅拌工艺,可获得金属半固态加工要求的细小、等轴分布均匀的非枝晶组织。即降低降体温度、搅拌速度及适当剪切时间有利于细小球形晶粒的形成。加大搅拌速度及合理搅拌时间可以细化晶粒,主要是由于是高剪切作用下熔体获得一个非常均匀温度场,从而增加有效形核的缘故。     

The refining effect of Fe-Ti-N master alloy towards 409L stainless steel

The Fe-Ti-N mater alloy was prepared through the in-situ reaction of nitrogen gas with the Fe-Ti melt.Scanning electron microscope results show that the particles uniformly distributed in the iron matrix were TiN.The deliberately prepared Fe-Ti-N master alloy was employed for the 409L ferritic stainless steel in an attempt to refine the as-cast solidification structure.It was found that the effectiveness of Fe-Ti-N master alloy on refining of the as-cast 409L ferritic stainless steel was affected by addition level,holding time and melts temperature.It was found that the average equiaxed grain size decreased from 1 503μm to 303μm,the proportion of equiaxed grain zone increased from 14%to 100%with increasing the Fe-Ti-N master alloy addition level to 2.5%.The proportion of equiaxed grain decreased from 85%to 4%as the solidification temperature increased from 1 803 K to 1 883 K.When the holding time reached to 8min,the solidification structures of 409L ferritic stainless steel show extreme points in the proportion of equiaxed grain.It is clear that the grain refining efficiency gradually fade away with the increasing of the holding time at the very beginning.However,when the holding time continues to increase and exceeds the extreme point, the grain refining efficiency of the Fe-Ti-N master alloy recovered to a certain degree.The experimental results mentioned above have been analyzed in terms of thermodynamics.Under appropriate conditions,the Fe-Ti-N master alloy used for grain refinement of the solidification structure of 409L ferritic stainless steel may have good prospects for industrial applications.     

Microstructure and mechanical properties of Mg-10Y-2.5Sm alloy

The microstructure and mechanical properties of aged Mg-10Y-2.5Sm alloy were investigated.The results showed that the microstructure of the alloy consisted of α-Mg matrix and Mg24Y5 phase,and fine Mg24Y5 particles distributed in α-Mg matrix uniformly and dispersedly.Sm enhanced α-Mg matrix and Mg24Y5 phase by solid solution effect.At 200-300 oC,the ultimate tensile strengths were more than 200 MPa and the elongations were about 3%.Compared with those at room temperature,the mechanical properties had no obvious changes.     

Mg-5Gd-3Y-0.8Zr合金的微观组织及耐NaCl溶液腐蚀性能研究

系统研究了Mg-5Gd-3Y-0.8Zr合金的微观组织和耐蚀性能,通过静态失重法测定了其在NaCl溶液中的腐蚀速率。结果表明:铸态合金主要由基体α-Mg和方块状β相(Mg_5Gd、Mg_(24)Y_5)组成,时效处理后分布在晶界处的共晶β相数量明显增加;在NaCl溶液中腐蚀12 h以后镁合金的腐蚀速率明显增加,在3.5%Na Cl(质量分数)溶液中腐蚀24 h后,镁合金已被严重腐蚀,表面布满腐蚀坑和未脱落的白色腐蚀产物;镁合金易产生沿晶腐蚀,方块状共晶β相颗粒可有效阻止表面腐蚀沿晶界向镁合金内部扩展,从而提高镁合金的耐蚀性。     

AZ31镁合金的研究现状

综述了国内外对AZ31镁舍金的研究现状。讨论了主要合金元素对AZ31镁合金的组织和性能的影响,介绍了AZ31镁合金的晶粒细化、塑性成形技术的研究现状。对AZ31镁合金的发展前景进行分析。     

挤压态AZ31B镁合金在超塑变形过程中的微观组织及力学性能研究

通过正向温挤压获得了细晶微观组织的AZ31B镁合金。研究了在310～460℃范围内,应变速率1×10-3～1×100/s下的超塑性流变行为。结果表明,在415℃、1×10-3/s的条件下AZ31B镁合金具有良好的超塑性,最大延伸率可达380%。应变速率敏感指数达到0.47。通过光学显微镜和扫描电镜（SEM）分别观察了AZ31B镁合金在超塑变形过程中的微观组织演变和断口形貌。晶界滑移机制为AZ31B超塑变形的主要机制。     

固溶温度对挤压态Mg-13Al-6Zn-4Cu合金组织与性能的影响

采用不同的固溶温度对挤压态Mg-13Al-6Zn-4Cu(质量分数,%)合金进行热处理,然后在(150℃/10 h)条件下进行时效处理,通过金相显微镜、扫描电镜及能谱分析、维氏硬度与极化曲线测试,研究固溶温度对挤压态合金显微组织、硬度与腐蚀性能的影响。结果表明:固溶处理促进晶界处的β-Mg_(17)Al_(12)相充分溶入α-Mg基体中。提高固溶温度使基体晶粒再结晶长大,逐渐缩小T-MgAlCuZn相心部的Cu元素富集区,改变β析出相的形态和分布,促进层片状β相在α-Mg晶界析出,从而提高时效态合金的硬度。但固溶温度超过420℃时,合金晶粒粗化并发生过烧。固溶温度升高导致合金腐蚀电位负移,腐蚀电流增大,腐蚀速率加快。     

Pb对AZ91镁合金铸态显微组织及力学性能的影响

采用扫描电镜观察、电子探针分析及拉伸性能测试等方法研究了Pb的添加对AZ91合金显微组织和力学性能的影响。结果表明,Pb能够细化AZ91镁合金中的d—Mg和β-Mgl7Al12的晶粒,抑制二次B的析出,且Pb可改善β-Mgl7Al12相形态和分布。Pb通过细晶强化增加了合金强度和硬度,使合金的断裂机制从脆性解理断裂转变为准解理断裂。     

AZ31-0.84%Sb合金的机械性能与变形特征

The mechanical properties and deformation features of AZ31-0.84% Sb alloy have been studied by means of the measurement of the properties and morphology observation. Results show that UTS of AZ31-0. 84% Sb alloy at room temperature is 297 MPa, a higher value of UTS is still maintained up to 189 MPa as temperature elevated to 200℃. One of the main reasons for enhancing UTS of the alloy is attributed to the high volume fraction of the precipitates dispersed in the matrix, including Mg3Sb2 phase, which effectively hindered the movement of dislocations during the elevated temperature deformation. The deformation mechanisms of AZ31-0. 84% Sb alloy are the twins and dislocations activated on basal and non-basal planes, a c dislocations may be activated on the basal and nonbasalplanes in twins regions, and some of the thinner twins may shear through the dense dislocations within the thicker twins.     

Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

The effects of Sm on the microstructure and mechanical properties of Mg-11 Gd-2 Y-0.6 Al alloy were investigated by X-ray diffraction,optical microscopy,scanning electron microscopy,energy dispersive spectrometry and high resolution transmission electron microscopy.Based on the theory of edge—edge matching and electronegativity theory,the mechanism of grain refinement is discussed.The strengthening mechanism is expounded conveniently from fine grain strengthening,coherent strengthening,precipitation strengthening and grain boundary strengthening.The results show that the micro structure of Mg-11 Gd-2 Y-0.6 Al alloy is mainly composed of a-Mg matrix,Mg_5 Gd and Mg_(24)Y_5 phases.The addition of Sm forms Mg_(41)Sm_5 phase in the alloy and refines the alloy.The addition of Sm significantly improves the mechanical properties of the alloy at room and high temperatures.When the addition of Sm is 3 wt%,the tensile strengths of the alloy at room temperature and high temperature(200℃) reach the maximum value 292 and 321 MPa,respectively.The fracture mode of the alloy at different temperatures is mainly brittle fracture and intercrystalline fracture.     

Deformation Structure of Unidirectionally Compressed Ultrafine-Grained Mg-3Al-1Zn Alloy

Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting grain size of twinning in the UFG AZ31 alloy is also given.     

Grain refinement of Mg-3Y alloy using Mg-10Al_2Y master alloy

The as-extruded Mg-10 Al_2 Y master alloy was chosen as a novel grain refiner for as-cast Mg-3 Y alloy.Contrast samples of cast Mg-3 Y alloy added with pure Al and Mg-Zr master alloy grain refiners were prepared under the same conditions.In this study,the influence of addition amounts of Al_2 Y and holding time on grain refinement efficiency as well as tensile properties was investigated.And the grain refining ability of the Al_2 Y particles was systematically evaluated in terms of the addition amounts,number density of the Al_2 Y particles and holding time.The finest grains are achieved at 2 wt% Al_2 Y addition amount,which corresponds to number density of the polygonal Al_2 Y particles of 420-460 mm~(-2).The Mg-10 Al_2 Y master alloy has significant refinement performance and no refining recession occurs at the holding time within 60 min,or the settling time up to 180 min.Grain refinement and the second phase strengthening of uniformly distributed Al_2 Y particles contribute to the simultaneous enhancement on both strength and elongation of Mg-3 Y alloy.     

Al—3B中间合金的加工量对亚共晶Al—Si合金晶粒细化的影响

研究了Al-3B中间合金不同的加入量对亚共晶Al-Si合金晶粒尺寸的影响。该中间合金对所研究全部范围内的Al-Si合金都具有一定的细化效果,但在不同的含硅量下其细化能力并不相同,同时证实对未经细化处理的亚共晶Al-Si合金而言,在含硅量约3%（质量分数,下同）时合金具有最小的晶粒尺寸。随着Al-3B中间合金加入量的提高,出现最小晶粒尺寸的合成成分向高硅方向移动,当加入量达到1%时,在含硅量为6%的Al-Si合金中出现最小的晶粒尺寸。     

原位反应合成技术在ZL201铸造铝合金中的应用

利用原位反应合成技术,以工业纯铝、氟钛酸钾和氟硼酸钾为原料制备了Al-Ti-B中问合金,结果表明,Al-Ti-B合金中AlB_2和Al_3Ti颗粒细小且弥散分布,对铝及铝合金具有显著的晶粒细化效果,并且能大幅度提高殂ZL201铸造铝合金的铸造性能和力学性能。