工艺参数和热处理对挤压铸造AZ91D力学性能的影响

通过试验研究了工艺参数和热处理对挤压铸造AZ91D合金力学性能的影响。结果表明:合理的工艺参数使AZ91D合金在普通冷室压铸机条件下可以获得良好的力学性能。且经固溶处理后其抗拉强度、硬度和伸长率都会提高,而经固溶时效处理后抗拉强度和硬度会进一步提高,但伸长率有所下降。     

等温热处理对AZ91D+Ce镁合金半固态组织的影响

研究了等温热处理对AZ91D+Ce镁合金半固态组织的影响,获得了较理想的球状或类球状晶粒组织。结果表明,在等温热处理的过程中,加入稀土Ce会阻碍原子向固相粒子聚集和结合,抑制固相颗粒的长大,形成细小圆整的半固态组织。随等温热处理温度的升高,原子活动能力增强,熔化速度加快,液相量增加,固相颗粒尺寸先减小后增大。在等温初始阶段,熔化对初生固相颗粒尺寸起决定作用,使得颗粒尺寸减小。但是,随等温时间的进一步增加,由于合并粗化和Ostwald熟化的作用,固相颗粒开始长大。     

Effect of isothermal heat treatment on semi-solid microstructure of AZ91D magnesium alloy containing rare earth Gd

The AZ91 D magnesium alloy containing rare earth Gd was prepared in this study, and the effect of semi-solid isothermal heat treatment on the microstructure of the alloy was investigated to obtain an optimum semi-solid structure. Results show that Gd can refine the microstructure of AZ91 D magnesium alloy, and the optimum semi-solid AZ91 D microstructure can be achieved by adding 1.5wt.% Gd. After treated at 585 °C for 30 min, the well distributed rose-shaped and near-spherical semi-solid microstructures of AZ91D+1.5wt.%Gd alloy can be obtained. The liquid phase of the semi-solid alloy consists of three components, namely, the molten pool, the entrapped liquid pool and the liner liquid film which separates two neighbor particles. The solid phase is composed of two phases, the primary α-Mg particles and the α-Mg phase formed in the second stage of solidification. With the increase of holding time, melting which causes the decrease of the primary α-Mg particle size is the dominant mechanism in the initial stage while coalescence and Ostwald ripening tend to be the principles later.     

等温热处理对消失模铸造AZ91D镁合金组织与性能的影响

对AZ91D镁合金消失模铸件进行了近半固态等温热处理,通过光学显微镜、扫描电镜以及金属拉伸试验对其组织和力学性能进行了研究.结果表明,AZ91D镁合金消失模铸件经过530 ℃×60 min近半固态等温热处理后,合金显微组织中β-Mg17 Al12相基本熔入基体,枝晶状的铸态组织在等温处理过程中变得均匀圆整,由此产生的固溶强化作用使材料的力学性能大大提高,抗拉强度达到213.17 MPa,屈服强度达到115.63 MPa,伸长率达到4.11%,等温热处理后的断口呈现明显的韧性断裂特征.     

AZ91D镁合金半固态铸轧工艺因素对组织的影响

在实验室半固态铸轧试验设备上进行了镁合金半固态铸轧试验,研究了AZ91D镁合金半固态铸轧组织的影响因素。结果表明,搅拌速度、铸轧温度对半固态镁合金组织有显著的影响。过快过慢的搅拌速度都不利于半固态组织的形成,试验表明搅拌速度300 r/min最佳;铸轧温度从高到低,固相率明显从小到大。     

触变成型镁合金铸件热处理显微组织的演变

通过金相显微镜、SEM及XRD等观察手段研究了触变成型AZ91D镁合金铸件固溶、时效处理时显微组织的演变。结果表明:触变成型AZ91D镁合金在415℃时固溶处理时β相溶解入α-Mg固溶体的速度比高压压铸的快。在固溶处理初期,铝元素从β相扩散至块状初生α-Mg相,导致块状初生α-Mg晶粒周围形成富铝晕圈。时效处理时,触变成型铸件在5h左右硬度达到峰值,高压压铸铸件在12h左右达到峰值。触变成型铸件时效析出方式存在片层状不连续析出和针状连续析出两种。     

热处理对浇铸和压铸AZ91D-RE镁合金组织与性能的影响

分别采用金属模浇铸和压铸方法制备了相同成分的AZ91D-RE合金,应用金相显微镜、X射线衍射仪、扫描电镜和硬度计分析和测试了热处理对合金组织和性能的影响,并对其耐腐蚀性能进行了探讨.结果表明,铸态下AZ91D-RE压铸合金组织由α-Mg和Mg17Al12相组成,而浇注合金中还出现了MgY相;经固溶处理后,压铸合金中的Mg17Al12相全部消失,而浇注合金中尚有部分Mg17Al12相未溶解;随着时效时间的延长,压铸镁合金的硬度先升高后下降,并在11 h达到最大值,而浇注镁合金的的硬度一直升高,表现为时效未完成;在相同条件下,压铸AZ91D-RE合金的组织比浇铸合金的细小,并且,压铸AZ91D-RE合金的耐腐蚀性能也均优于浇铸合金的.     

热处理对压铸镁合金化学镀层组织和性能的影响

采用化学镀方法在AZ91D压铸镁合金表面获得N i-P镀层,研究了不同热处理温度对镀层的组织和性能的影响。结果表明:镍层中P含量为6.22 wt%,镀层组织为非晶+少量纳米晶组织。随热处理温度升高原始镀层中的非晶组织中先形成镍纳米晶,然后纳米晶镍伴随晶化过程进行迅速长大,并在镍基体上析出N i12P5和N i3P相。镀层与基体的结合强度在350℃附近达最大结合强度为3.7 MPa,镀层硬度在400℃附近达最大值为825 HV;盐雾腐蚀实验表明镀层耐腐蚀性能良好,连续盐雾8 h未出现腐蚀斑点。经过不同的热处理,镀层的耐蚀性随着热处理温度的提高而下降。     

挤压铸造准晶增强AZ91D镁基复合材料组织与性能

为了改善AZ91D镁合金的性能,采用挤压铸造法制备了Mg-Zn-Y准晶中间合金增强AZ91D镁基复合材料,研究了准晶中间合金含量对复合材料组织和性能的影响。结果表明挤压铸造工艺可以有效细化晶粒,复合材料的显微组织主要由α-Mg基体、晶界上分布的β-Mg17Al12相以及Mg3Zn6Y准晶颗粒组成,准晶颗粒和α-Mg基体之间形成稳定结合。当准晶中间合金含量为5%时,抗拉强度和断后伸长率达到最大值,分别为194.3MPa和9.2%。复合材料的强化机制为细晶强化和准晶颗粒强化。     

固溶时效对半固态挤压SiC/AZ91D组织与性能的影响

为了获得综合力学性能良好的镁基复合材料,采用近液相线保温法制备10 μm 15％SiC/AZ91D(质量分数)半固态坯料进行半固态挤压后得到其复合材料,再经过415℃固溶处理24 h(T4)和进一步220℃时效处理8 h(T6).结果表明:随着固溶时效的进行,晶界处的层片状和点状Mg17Al12相溶解,然后在晶粒中二次...     

高压热处理对AZ91D镁合金组织的影响

采用高压六面顶压机对AZ91D镁合金进行热处理。使用X射线衍射仪、金相电镜、场发射扫描电镜研究热处理压力对AZ91D镁合金微观组织的影响。结果表明,高压热处理后的镁合金的仍由基体α-Mg和β-Mg17Al12相组成,但高压热处理后β-Mg17Al12相的形态和分布发生了明显变化。随着压力的增大,β-Mg17Al12相析出量减少,Al原子在基体中的固溶度增加。此外,高压热处理可细化晶粒,压力为2 GPa时效果最佳。     

AZ91D镁合金在半固态等温热处理中的组织演变

研究了未变质处理和变质处理的AZ91D镁合金在半固态等温热处理过程中的组织演变,并对其组织演变机理进行了探讨。结果表明：AZ91D镁合金在液－固相区570℃等温处理时,未变质处理的δ相由粗大的树枝晶演变为大块状,随后δ相发生熔化分离,并在半固态等温过程中演变为球状,产生相最小尺寸可达50－80μm;变质处理的初生δ相由等轴晶演变为小块状,随后进一步熔化分离为更细小的斑块,接着逐渐演变为球状组织,初生相最小尺寸可达20－60μm。等温处理时间过长时,两种组织都会发生合并长大。     

半固态铸轧AZ91D镁合金板带的再加工组织性能

实验研究了半固态铸轧成形技术制备的AZ91D镁合金板带的再加工组织性能及特点。半固态铸轧实验是在自制的试验机上进行的,得到半固态铸轧AZ91D镁合金板带之后,分别进行冷轧、热轧和冲杯实验,加工后取样观察显微组织。实验结果表明,半固态铸轧的AZ91D镁合金板带材具有较好的加工性,最大冷变形可达到28%,热变形可达到47%。观察组织可见,横断面、纵断面固相颗粒在轧制作用下都有所变形,纵断面的变形更为严重,说明组织沿轧制方向塑性变形较大。     

Reheating microstructure of refined AZ91D magnesium alloy in semi-solid state

By means of equal channel angular extrusion (ECAE) test, upsetting test and metalloseope, reheating mierostruetures of raw casting ingots, materials prepared by SIMA and materials extruded by ECAE in semi-solid state were investigated. The results show that compared with those of raw casting ingots and materials prepared by SIMA, reheating microstrueture of materials extruded by ECAE is the best and the final grain size is the finest. With increasing holding time, a growing phenomenon occurs in reheating microstrueture of materials extruded by ECAE, which can be described by Ostwald ripening law. The average grain size increases firstly, subsequently decreases and the shape factor of grains approaches to 1 as the reheating temperature increases. With increasing equivalent strain, the average grain size decreases. This demonstrates that reheating material extruded by ECAE technology is a good method to prepare AZ91D magnesium alloy semi-solid billets.     

Effect of heat treatment on the microstructure and mechanical properties of the consolidated Mg alloy AZ91D machined chips

Influence of heat treatment on the properties of the consolidated AZ91D Mg alloy chips was performed in this study. The chips were pressed into a die to form a compact with a green density of 1.6 g/cm³. The 50-mm diameter green compact was then extruded into a 20-mm rod at 350 °C. The extruded rod was solution treated at a temperature of 415 °C for 24 h; the solution treated specimens were then aged at two temperatures: 170 and 215 °C. Heat treatments were conducted to explore the microstructure evolution and mechanical properties of the extruded rod. Heat treatments revealed that the age hardening effect was related to the transformation of the microstructure. Over aging during age heat treatment was believed to be caused by the formation of a lamellar structure composed of alternating layers of Mg₁₇Al₁₂ phase and magnesium matrix.     

半固态AZ91D镁合金压铸过程的数值模拟

采用机械搅拌方式研究了半固态AZ91D合金的流变特性,并根据实验数据,拟合出剪切速率为238s-1时,半固态AZ91D合金的固相体积分数和表观粘度之间的关系式。从流体力学的角度,采用数值技术对半固态AZ91D镁合金的压铸过程进行了研究。数值模拟结果表明,半固态浆料温度为550℃、模具温度为300℃、压铸速度为1m/s时,该文所设计的压铸件的压铸过程能很好地进行。同时,该研究工作能为分析压铸成形过程提供有益的信息。     

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like α-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, α-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in cavity, microstructural segregation of unmelted α-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.     

热处理对压铸AZ91D合金组织及硬度的影响

研究在线淬火、离线固溶处理(420℃×1 h在水中快冷)和时效处理(190℃×4 h空冷)对压铸AZ91D镁合金组织及硬度的影响。结果表明:在线淬火和离线的时效处理可提高压铸AZ91D合金的布氏硬度,但是离线固溶处理使合金硬度下降;在线淬火和时效处理后合金的组织与压铸AZ91D基本相同,仍由α-Mg及β-Al12Mg17组成。在压铸镁合金冷却过程中在线淬火使温度急剧降低,增强了Al元素固溶强化的效果;而时效处理通过Al12Mg17分解后重新析出并细化了晶粒,增强了细晶强化的效果。离线的固溶处理Al12Mg17分解后虽然固溶强化效果增强但是晶界强化相大幅减少,导致合金硬度降低。     

La-Ce混合稀土对AZ91D合金组织和性能的影响

以AZ91D镁合金作为研究对象,探究了La-Ce混合稀土含量对其组织性能的影响。结果表明:在AZ91D镁合金中加入混合稀土La-Ce后,铸态组织为网状β-Mg₁₇Al₁₂相及少量杆状稀土化合物。且随着稀土含量增多,β-Mg₁₇Al₁₂和杆状稀土化合物被细化。经固溶时效处理后,随稀土含量增加,试验合金伸长率增大,硬度和抗拉强度均先增后降,稀土含量为2.38%时,合金力学性能最佳。     

Effect of cenospheres addition on microstructure and properties of AZ91D alloy

The cenospheres/AZ91D composites were fabricated by melt stir method. The phases, microstructure and tensile fracture morphology of the composites were analyzed using XRD, Olympus metallurgical microscopy and SEM methods. The thermal expansion coefficient(CTE) and tensile properties were measured. The results showed that the cenospheres distribute uniformly in the Mg alloy matrix and refine the matrix microstructure. Mg2 Si and MgO were found in addition to α-Mg and β-Mg17Al12 phases using XRD. The CTE of the composites reduced after the cenospheres are added. The yield strength of the composites increases significantly with an increase in the mass fraction and a decrease in the size of the cenospheres. The tensile strength of the composites achieves maximum when the mass fraction of cenospheres is 9wt.% and the size of cenospheres is 80 μm. The fracture mechanism of the composites is cleavage fracture.