不同铸轧工艺参数对铸轧微观组织的影响

在实验铸轧机上对不同铸轧条件下铸轧微观组织的变化规律进行研究。结果表明,不同铸轧速度、铸轧厚度铸轧出的变形组织不同。当铸轧速度为0.9 m/min、厚度为6 mm时,变形组织沿纵向出现典型的加工流线,横向为变形压扁后的晶粒,但没有产生再结晶现象,TEM表明,变形体内的位错密度较低,形成了亚晶粒;当铸轧速度为2.6 m/min、厚度为3 mm时,铝带坯表层比心部的变形程度严重,在薄铝带坯表层金属中出现不完全动态再结晶晶粒,TEM表明,在亚晶界附近存在大量的位错塞积和位错缠结,在亚晶内分布着二维位错网。

热变形方式对2D70耐热铝合金组织与性能的影响

分别采用常规变形方式(直接挤压)、强变形方式(3次多方锻造与挤压变形相结合)制备了大规格2D70耐热铝合金棒材,利用金相显微镜、透射电镜、力学性能测试、电导率测试等手段对比分析了两种工艺所获得棒材的变形态、固溶态显微组织特征以及195℃人工时效强化特性差异。结果表明,与传统直接挤压方式相比,采用强变形工艺所获得的基体组织相对均匀,合金中各类第二相破碎严重、分布合理;经强变形破碎的Al2CuMg、Al2Cu等可溶第二相可在固溶处理过程中充分回溶以提高时效强化潜力,同时,Al9FeNi、Al7Cu4Ni等难溶第二相的尺寸、形态与分布通过强变形得以合理调控,使得合金棒材在195℃人工时效的过时效阶段具有更优越的抗过时效能力,合金热稳定性较好。

Ti60合金热变形过程中的软化机制

采用Thermecmaster−Z型热加工模拟试验机对Ti60合金进行等温恒应变速率压缩实验,通过分析流动应力−应变曲线的流动特征,计算加工硬化率,观察变形微观组织,并结合变形激活能的计算,研究该合金在变形温度为850~950℃、应变速率为0.001~10 s^−1、真应变为0.51热变形条件下的软化机制。结果表明:Ti60合金在低应变速率(0.001~0.1 s^−1)和高应变速率(1~10 s^−1)区间流动应力−应变曲线分别呈现流动稳态型和流动软化型两种;加工硬化率曲线呈现无拐点特征;变形微观组织为动态回复组织,未出现动态再结晶现象;变形激活能在低应变速率区间和高应变速率区间分别为484.35 kJ/mol和500.76 kJ/mol,两者相差不大。综合这些结果可以判定,Ti60合金的软化机制以动态回复为主。

超声表面滚压处理对AZ31B镁合金组织和性能的影响

目的研究AZ31B镁合金在超声表面滚压处理后,表面微观结构、显微硬度和表面粗糙度的变化及其在拉伸试验过程中对AZ31B镁合金内部组织的影响。方法利用超声表面滚压处理在AZ31B镁合金表面制备梯度变形层。利用X射线衍射仪、EBSD、显微硬度仪和表面粗糙度仪,分析试样表面的微观结构、显微硬度和表面粗糙度。对超声表面滚压处理前后试样进行拉伸试验,分析其拉伸性能和微观组织变形。结果经过9道超声表面滚压处理后,样品表层形成了厚约600μm的变形层。变形层组织呈梯度分布,分别为超细晶粒层、细粒过渡层和母材组织。随着与试样表面距离的增加,试样表面的显微硬度值为84~52HV10g。USRP试样的表面粗糙度Ra达到0.140μm。在拉伸过程中,相对于母材,超声表面滚压处理试样微观组织的变化量较少。结论相对于未处理试样,超声表面滚压处理试样的屈服强度提高了28%,显微硬度提高了40%,表面粗糙度降低了96.4%。同时,超声表面滚压处理在镁合金试样表层形成的梯度结构,在拉伸过程中降低了中心微观组织的变形。

高强抗震钢筋原位拉伸的微观组织变形机理

为研究不同组织对高强度抗震钢筋性能的影响,得到其微观组织变形行为的规律,针对3种不同组织特征的500MPa级高强度抗震钢筋,其组织分别为铁素体和珠光体、铁素体和珠光体以及少量贝氏体、铁素体和少量珠光体以及大量贝氏体为主,利用原位拉伸仪观察、研究多相微观组织变形行为以及多相组织协调变形机理以及断裂机制。结果表明,铁素体和珠光体为主的试验钢,铁素体和珠光体变形明显,其中铁素体优先变形,但由于贝氏体硬质相对珠光体的阻碍作用,变形不明显,随着变形量的增加,最后导致珠光体的断裂。以铁素体和珠光体以及少量贝氏体为主的试验钢,贝氏体在初期基本不变形,而后对铁素体和珠光体的变形产生阻碍运动,仅发生一定程度的改变。以铁素体和少量珠光体以及大量贝氏体为主的试验钢,变形初期以铁素体变形为主,珠光体因其含量非常低,变形不明显。随变形量的增加,贝氏体的变形越发明显,到一定程度后促使珠光体开始变形,并最后断裂。

Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy

Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

Characterization of hot deformation microstructures of alpha-beta titanium alloy with equiaxed structure

Hot deformation behavior and microstructure evolution of TC11（Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） alloy with equiaxed structure were investigated in the two-phase field at temperatures in the range of 980-800 ℃ and at strain rates of 0.001 s-1,0.01 s-1,0.1 s-1.Effects of thermo-mechanical parameters on both of the stress—strain curves and microstructure evolution were analyzed.Grain boundary characteristics of deformation microstructures were tested by electron backscattered diffraction（EBSD）.The results reveal that β-phase dominates the deformation and presents discontinuous dynamic recrystallization at 980 ℃;meanwhile,α-phase coarsens at lower strain rates and dissolves at higher strain rates,and α-phase volume fraction and grain size decrease with increasing strain rate.Super-plastic deformation occurs at 950-900 ℃ and strain rate of 0.001 s-1.And the deformation is dominated by soft β-phase,phase interfaces and grain boundaries.Microstructural mechanism operated at 850 ℃ is continuous dynamic recrystallization of α-phase that dominates the deformation,and β-phase deforms to match the deformation of α-phase.

冷拔<110>单晶铜的形变织构和微观组织演变

采用电子背散射衍射(EBSD)和透射电子显微镜(TEM)对冷拔<110>单晶铜的织构和微观组织进行了分析.为了考察初始取向对冷拔铜线材形变组织和织构的影响,<110>试验结果并与冷拔<100>和<111>单晶铜的结果进行了对比.发现与<100>和<110>单晶铜相比,<110>单晶铜晶粒分裂更加明显,在冷拔过程中迅速形成<100>+<111>织构.但高应变下,由于剪切应力的影响,<100>和<111>织构组分沿线材径向的分布并不均匀,<100>织构绝大部分分布在试样表面,<111>则主要分布于试样中心.冷拔<110>单晶铜的微观组织研究结果表明,在低应变情况下,可表征为两类非晶体学几何必须位错界面,随变形量的增加,大量S带开始出现,高应变时,绝大部分位错界面已与冷拔方向平行,形成薄片状组织.与<100>和<111>单晶铜相比,冷拔<110>单晶铜的几何必须位错界面的平均失配角和平均间距更大.由于<110>单晶铜中同一织构组分内仍能形成高角度界面,在位错界面失配角分布图中很快形成双峰分布.

Hot deformation behavior and microstructural evolution of Al-Zn-Mg-0.25Sc-Zr alloy during compression at elevated temperatures

The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.

ECAP中摩擦因数对7075铝合金变形及组织的影响

采用有限元软件DEFORM-3D对7075铝合金等通道角挤压(ECAP)过程进行数值模拟,分析了不同摩擦条件下载荷变化、变形行为以及等效应力应变分布情况,并利用7075铝合金动态再结晶模型对微观组织变化过程进行了预测。结果表明,随着摩擦因数增大,载荷峰值明显增大甚至成倍增长,且载荷值波动加剧,试样"端部效应"减弱,等效应力应变分布不均匀;试样中部稳定变形区晶粒随挤压道次增多而不断细化,试样与通道接触部位形成晶粒细小区,经过4道次挤压后,摩擦因数为0.4时稳定变形区的晶粒比摩擦因数为0.1时的细小。

Effects of technical parameters of continuous semisolid rolling on microstructure and mechanical properties of Mg-3Sn-1Mn alloy

A sloping semisolid rheo-rolling process of Mg-3Sn-1Mn alloy was developed, and the effects of process parameters on the microstructure and mechanical properties of Mg-3Sn-lMn alloy strip were studied. The results show that the primary grain average diameter of the strip increases with the increase of the roll speed. The primary grain average diameter decreases firstly and then increases with the increase of the vibration frequency, and the tensile strength and elongation of the strip increase firstly and then decrease with the increase of the vibration frequency. The primary grain average diameter increases with the increase of casting temperature, and the tensile strength and elongation of the strip decrease correspondingly. When the casting temperature is 670℃, the roll speed is 52 mm/s, and the vibration frequency is 60 Hz, Mg-3Sn-1Mn alloy strip with good properties is produced. The mechanical properties of the present product are higher than those of Mg-3Sn-lMn alloy casting with the addition of 0.87% Ce （mass fraction）.

Microstructure control of AZ31 alloy by self-inoculation method for semisolid rheocasting

A novel rheocasting process, self-inoculation method （SIM）, was developed for the microstructure control of semisolid wrought Mg alloy. This process involves mixing between liquid alloy and particles of solid alloy （self-inoculants）, subsequently pouring the mixed melt into a special designed multi-stream fluid director. The primary phase with dendritic morphology in the conventionally cast AZ31 alloy has readily transformed into near spherical one in the slurry produced by SIM from melt treatment temperature between 690 ℃ and 710 ℃ and self-inoculants addition of 3%-7%. Achievement of the non-dendritic microstructure at the higher melt treatment temperature requires more self-inoculants addition or decreases in the slope angle of fluid director. Primary phase in the slurry thus produced has attained an ideally globular morphology after isothermal holding at 620 ℃ for 30 s. The increasing holding time leads to decrease of shape factor but the coarsening of particle size. The spheroidization and coarsening evolution process of solid particles during the isothermal holding were analyzed by Lifshitz-Slyozov-Wagner （LSW） theory.

Dislocation density model and microstructure of 7A85 aluminum alloy during thermal deformation

The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate(0.001−1 s^(−1))and deformation temperature(250−450°C)was studied by optical microscopy(OM)and electron back scattering diffraction(EBSD).Based on the K-M dislocation density model,a two-stage K-M dislocation density model of 7A85 aluminum alloy was established.The results reveal that dynamic recovery(DRV)and dynamic recrystallization(DRX)are the main mechanisms of microstructure evolution during thermal deformation of 7A85 aluminum alloy.350−400°C is the transformation zone from dynamic recovery to dynamic recrystallization.At low temperature(≤350°C),DRV is the main mechanism,while DRX mostly occurs at high temperature(≥400°C).At this point,the sensitivity of microstructure evolution to temperature is relatively high.As the temperature increased,the average misorientation angle(θˉ_(c))increased significantly,ranging from 0.93°to 7.13°.Meanwhile,the f_(LAGBs) decreased with the highest decrease of 24%.

Influence of dispersoids on grain subdivision and texture evolution in aluminium alloys during cold rolling

Al-Mn alloys containing similar amounts of solutes but various dispersoid densities were cold rolled. The grain subdivision and micro-texture were examined by electron backscatter diffraction and orientation imaging microscopy. Macro-texture was measured by X-ray diffraction. It is found that a high density of fine dispersoids enhances the development of the copper and S textures at large strains （～3）, and also induces a higher fraction of high-angle grain boundaries. At smaller strains, the texture and high-angle grain boundaries are not evidently influenced by the density of dispersoids. It is suggested that the texture evolution, which is enhanced by dispersoid pinning effect, contributes to the grain subdivision and the formation of high-angle grain boundaries.

Microstructure evolution of 7050 aluminum alloy during hot deformation

Hot compression of 7050 aluminum alloy was performed on Gleeble 1500D thermo-mechanical simulator at 350 ℃ and 450 ℃ with a constant strain rate of 0.1 s-1 to different nominal strains of 0.1, 0.3 and 0.7. Microstructures of 7050 alloy under various compression conditions were observed by TEM to investigate the microstructure evolution process of the alloy deformed at various temperatures. The microstructure evolves from dislocation tangles to cell structure and subgrain structure when being deformed at 350 ℃, of which dynamic recovery is the softening mechanism. However, continuous dynamic recrystallization (DRX) occurs during hot deformation at 450 ℃, in which the main nucleation mechanisms of DRX are subgrain growth and subgrain coalescence rather than particle-simulated nucleation (PSN).

Deformation behaviour and microstructure evolution of AlMg6Mn alloy during shear spinning

Deformation behavior and microstructure of AlMg6Mn alloy subjected to shear spinning were studied by means of mechanical characterization, optical and SEM＋EDS microscopy. Specimens were shear spun on an industrial spinning machine using different mandrels, providing reductions of wall thickness of 30%, 50% and 68%. The grain structure developed during shear spinning refines gradually. The grains elongate in axial direction with increase of reduction, and also stretches along circumferencial direction. Optimal combination of strength and elongation is observed. This is attributed to grain refinement and dislocation reactions with particles and atoms of Mg and Mn in solid solution.

Influence of temperature and strain rate on hot deformation behavior of Zr_(50)Ti_(50) alloy in single β field

The deformation behavior and microstructure of the Zr50Ti50 alloy in β phase field were investigated by isothermal compression tests at temperatures ranging from 700 to 850 °C and strain rates ranging from 0.001 to 1 s?1. The flow curves exhibited typical flow softening. The initial discontinuous yielding behavior was observed at higher strain rates, which was not found in other traditional Zr alloys. The apparent deformation activation energy was calculated to be 103 kJ/mol and constitutive equationdescribing the flow stress as a function of the strain rate and deformation temperature was proposed. The analysis indicated that the hot deformation mechanism was mainly dominated by dynamic recovery. However, dynamic recrystallization was delayed by dynamic recovery. Thereafter, the processing map was calculated to evaluate the efficiency of the forging process at the temperatures and strain rates investigated and to optimize processing parameters of hot deformation. The optimum processing parameters were found to be 830?850 °C and 0.56?1 s?1 for hot the deformation of Zr50Ti50 alloy in the β phase region.