AZ31B镁合金板液压-机械拉深试验研究

对AZ31B镁合金板进行液压-机械拉深试验,分析其变形特点和液压力对其成形性能的影响规律,并对液压拉深件的破裂现象进行了分析.试验结果表明,AZ31B镁合金板在液压-机械拉深时的成形性能比普通拉深时的差,主要原因是AZ31B镁合金板本身的塑性变形能力差,液压力未能及时发挥作用.     

AZ31B镁合金板径向推力充液拉深试验

镁合金板冷成形性能差,采用液压成形的方法可提高其冷成形性能。对AZ31B镁合金板进行径向推力充液拉深试验,分析液压力大小、模具尺寸和坯料尺寸对最大拉深高度的影响规律,并对液压拉深件破裂位置、裂纹走向及裂纹形态进行分析。研究结果表明,当凸模圆角半径较大时,随着液压力的增大,得到的最大拉深高度也大;凸模圆角半径较小时,仅有当液压力大小合适时,才能改善其成形性能;板坯直径越大,最大拉深高度就越小。破裂位置一般在拉深试件的底部圆角、凸缘和侧壁处,且裂纹走向、裂纹断面呈现不同的形态。     

Mechanical anisotropy and deep drawing behaviour of AZ31 and ZE10 magnesium alloy sheets

The influence of the initial microstructure on the deep drawability and the associated microstructural evolution in two different magnesium alloy sheets, AZ31 and ZE10, has been examined. Tensile testing at room temperature shows that the AZ31 sheet has high plastic strain ratios, r = 2–3, which are caused by strong basal-type texture. The ZE10 sheet shows lower r values, r ～ 1, as a result of its weak texture. Deep drawing experiments carried out over the temperature range 100–300 °C revealed that the ZE10 sheet can be successfully deep-drawn at lower temperatures than the AZ31 sheet. The ZE10 cups show earing despite the weak texture and low normal anisotropy, while earing of the AZ31 cups is negligible. In the ZE10 cups, deformation is accommodated mainly by 〈a〉 slips and by compression as well as secondary twinning. The occurrence of dynamic recrystallization is observed in successfully deep-drawn AZ31 cups.     

Deep drawing of square cups with magnesium alloy AZ31 sheets

The square cup drawing of magnesium alloy AZ31 (aluminum 3%, zinc 1%) sheets was studied by both the experimental approach and the finite element analysis. The mechanical properties of AZ31 sheets at various forming temperatures were first obtained from the tensile tests and the forming limit tests. The test results indicate that AZ31 sheets exhibit poor formability at room temperature, but the formability could be improved significantly at elevated temperatures up to 200 °C. The test results were then employed in the finite element simulations to investigate the effects of process parameters, such as punch and die corner radii, and forming temperature, on the formability of square cup drawing with AZ31 sheets. In order to validate the finite element analysis, the deep drawing of square cups of AZ31 sheets at elevated temperatures was also performed. The experimental data show a good agreement with the simulation results, and the optimal forming temperature, punch radius and die corner radius were then determined for the square cup drawing of AZ31 sheets.     

AZ31B镁合金方盒形件的差温拉深成形

以AZ31B镁合金方盒形件差温拉深成形过程为研究对象,进行了单向拉伸试验,确定了本构方程中的有关参数;依据差温拉深成形的特点,对影响AZ31B镁合金方盒形件拉深成形效果的重要指标进行了数值模拟,确定了最佳的凸模和凹模温度组合为50℃和250℃,并通过试验进行了验证;对较优温度组合条件下所得的试件进行了相关区域的金相组织分析,结果表明,塑性变形后的AZ31B镁合金方盒形件的组织性能明显优于原始板料,差温导致的孪晶可有效提高成形深度。     

Simulation of earing during deep drawing of magnesium alloy AZ31

Magnesium alloys develop pronounced crystallographic texture and plastic anisotropy during rolling, which leads to earing during deep drawing of the rolled sheets. This phenomenon is modelled for the magnesium alloy AZ31 using the finite-element method in conjunction with a viscoplastic self-consistent texture model. To determine the model parameters the model is adjusted to measured stress–strain curves in tension and compression. The predicted earing pattern is found to depend not only on the initial texture at the beginning of the drawing process, but to a large extent also on the evolution of texture during drawing.     

Deformation behaviors of magnesium alloy AZ31 sheet in cold deep drawing

To investigate how the popular magnesium alloy AZ31 sheet （aluminum 3%, zinc 1%） behaves in cold working, deep drawing experiments at room temperature, along with finite element（FE） simulation, were performed on the cold forming sheet of the AZ31 alloy after being annealed under various conditions. The activities were focused on the fracture pattern, limit drawing ratio（LDR）, deformation load, thickness distribution, anisotropic effect, as well as the influences of the annealing conditions and tool configuration on them. The results display that punch shoulder radius instead of die clearance, has much influence on the thickness distribution. The anisotropy is remarkable in cold working, which adversely impacts the LDR. The fracture often happens on the side wall at an angle to axis of the deformed specimen. The results also imply that the LDR for the material under present experimental conditions is 1.72, and annealing the material at 450 ℃ for 1 h may be preferable for the cold deep drawing.     

镁合金AZ31B板材热拉深成形工艺参数优化

在不同温度、不同压边力和不同拉深速度下，针对厚度为0．8mm的AZ31B镁合金板材的成形性能用有限元分析软件进行模拟与分析。在25～220℃的温度范围内，采用直径为140mm的坯料进行冲压成形，研究成形温度、拉深速度以及压边力对AZ31B镁合金板成形性能的影响。结果表明：成形温度为200℃时的极限拉深比达到了2.8；成形温度在200℃以下时，随着成形温度的升高。镁合金板材的成形性能越来越好。这证明AZ31B镁合金具有良好的热拉深性能；此外，拉深速度和压边力对AZ31B镁合金的拉深成形也有重要影响。     

High temperature composite forming limit diagrams of four magnesium AZ31B sheets obtained by pneumatic stretching

Formability of four magnesium AZ31B sheet materials, produced either by direct chill or twin roll continuous casting, was investigated at 400 °C and 5 × 10⁻³ s⁻¹ using pneumatic stretching. Sheet specimens were deformed through a series of four elliptical die inserts, with aspect ratios ranging between 1.0 and 0.4, producing ellipsoidal domes with different biaxial strain combinations. Testing was carried out in two scenarios, i.e. with the major strains aligned either along or across the rolling direction of the material. Circle grid analysis was then used to map the planar strains of the deformed specimens; the latter were used to generate comprehensive material forming limits curves (FLCs) that bound the safe, marginal and failure deformation zones. Orientation effects were quantified by constructing a “composite FLD” for each of the four sheets; the diagrams collectively showed that greater formability limits are achieved along the material's rolling direction. Furthermore, detailed comparisons between the four sheets were carried out based on formability limits, deformation uniformity, maximum dome height prior to failure, and fracture surface morphology and chemistry. Disparities in formability were linked to differences in grain structure and material inhomogeneities.     

AZ31B镁合金板材冲压成形性能研究

由于镁合金板材的冲压产品具有较好的力学性能和表面质量而成为镁合金材料应用的一个趋势。然而,目前它的许多成形性能参数尚未研究,这也影响了镁合金冲压成形工艺的设计。为丁研究镁合金薄板的冲压成形性能,试验得到了一些成形性能参数,并为镁合金冲压成形的有限元模拟提供了重要的试验参数。     

AZ31镁合金热成形过程中的本构关系

利用Gleeble-1500D热模拟试验机对AZ31镁合金在温度为300℃、350℃、400℃,应变速率为0.001 s-1～1.0s-1,每道次的变形量分别是:30%,10%,10%,总变形量为43%条件下,进行了高温多道次压缩试验。测量了不同应变速率下的应力-应变曲线。根据热模拟试验数据,确定AZ31镁合金高温变形本构关系模型,该本构关系模型的相对计算误差小于8%。试验确定的AZ31镁合金本构关系模型的适用温度范围为300℃～400℃,应变速率范围为0.001 s-1～1.0 s-1。得出动态再结晶激活能为207.61 kJ/mol。     

Experimental studies of deep drawing of AZ31B magnesium alloy sheet under various thermal conditions

The effect of temperature and temperature gradient within the blank on formability of AZ31B-O magnesium alloy is investigated. The effect of blank size on the success of isothermal deep drawing is studied. As blank size increases, forming under isothermal conditions becomes more difficult. To address this issue, non-isothermal forming is investigated and a formability window is identified in which the temperature at the punch nose must lie below the flange temperature to promote enhanced drawability, but above the temperature for activation of non-basal slip systems (to avoid low temperature fracture). The effect of punch speed on the forming forces, thickness and strain distribution within the formed cup is also investigated. At higher punch speeds, small cracks initiate at the punch radius region which increases the possibility of failure. Finally, the fracture surfaces from each thermal condition are observed using scanning electron microscopy. It is demonstrated that the fracture mechanism during deep drawing of magnesium alloy AZ31B is dependent on the forming temperature which controls the active deformation mechanisms.     

Warm incremental forming of magnesium alloy AZ31

Industrial application of magnesium alloy AZ31 is dramatically increasing due to the very competitive mechanical strength vs. weight ratio. On the other hand, AZ31 is very difficult to be formed at room temperature. In this study incremental forming of the above material is taken into account, with particular reference to formability limits. The role of the main process parameters on material formability was investigated through a wide experimental campaign and a rigorous statistical analysis.     

Influence of anisotropy of the magnesium alloy AZ31 sheets on warm negative incremental forming

Single point incremental forming of the magnesium alloy AZ31 sheets, which were fabricated by hot extrusion, slab + hot/cold rolling, strip-casting rolling and cross-rolling, respectively, was investigated at elevated temperatures. The results show that the anisotropy of the sheets fabricated by casting slab + hot/cold rolling and cross-rolling is not remarkable, and the formability is improved significantly. The circular, square and rotary cone parts were performed with satisfactory surface quality and without any microcracks successfully, and which is superior to those of the extruded sheet and the one-way rolled sheet. Therefore, anisotropy of the sheets has remarkable effects on the surface quality of the formed parts, and the effect becomes weakened with increasing temperature. It is proposed that cross-rolling sheet is much more suitable for warm SPIF process.     

Experimental and numerical study of warm deep drawing of AZ31 magnesium alloy sheet

Warm forming of magnesium alloy sheet has attracted more and more attention in recent years. The formability of magnesium alloy sheet at elevated temperature depends on appropriate processes, and the fabrication of high-performance sheet. In this research, an AZ31 magnesium alloy sheet with excellent performances is fabricated by the cross-rolling and the uniform annealing treatments. The uniaxial tensile tests are conducted using a Gleeble 3500 thermal–mechanical simulator, and the mechanical properties of AZ31 magnesium alloy sheet are analyzed. Finally, some limiting drawing ratio (LDR) experiments are performed. The experiments show that the LDR can reach 2.0 at the forming temperature of 150 °C and the drawing velocity of 15 mm/s. A warm deep drawing process is also simulated by the finite element method. The influences of drawing temperature and blank holder force on the formability are numerically investigated. The simulation demonstrated that variable blank holder force technology can improve the LDR from 3.0 to 3.5, and decrease the wall thinning ratio from 15.21% to 12.35%.     

AZ31镁合金板材室温拉深破裂行为

为了探索提高AZ31镁合金板材室温冲压性能的途径,通过断口形貌分析,对板材室温拉深变形过程中的破裂机理进行了研究.结果表明,室温下,对于普通轧制板材,在拉深比达到1.2后即在冲头肩部发生破裂;对于等径角轧制板材.其拉深比可达1.6以上;当拉深比达到1.8时,在杯形件凸缘发生破裂,断面光滑平整.为解理断裂.这主要与板材在拉深变形中的应力应变状态和其非基面织构有关.单向拉伸与断口分析表明其冲压性能和破裂行为的差异,主要是因为这两种板材织构不同所致.     

AZ31B镁合金盐浴碳氮钒共渗工艺

为提高AZ31B镁合金的表面硬度,改善其摩擦磨损性能及耐蚀性能,采用盐浴碳氮钒共渗工艺在AZ31B镁合金表面形成高硬度碳、氮化合物渗层,并用数字显微硬度计、光学显微镜、X射线衍射仪、X射线能谱仪、摩擦磨损试验和电化学测试分析渗层表面硬度、截面显微形貌、渗层表面物相组成、耐磨性和耐蚀性等。结果表明,盐浴碳氮钒共渗处理使AZ31B镁合金表面形成主要由VC、VN等高硬度金属化合物组成的渗层,渗层表面硬度最高达到283.1 HV0.05,相比原始试样和碳氮共渗处理试样分别提升280%和62%;相比原始试样,碳氮钒共渗试样的摩擦因数和磨损量分别降低约30%和50%,自腐蚀电位提高60 mV,自腐蚀电流密度降低一个数量级,表明盐浴碳氮钒共渗工艺能够显著提高AZ31B镁合金的表面硬度,提升其摩擦磨损性能及耐蚀性能。     

Texture evolution of extruded AZ31 magnesium alloy sheets

The evolution of texture during the annealing and hot rolling process of extruded AZ31 magnesium alloy sheets was studied. There are two kinds of texture components in the extruded AZ31 sheets. One is {0002}<1-010> and the other is {1-010}<1-120>. The {0002}<1-010>component predominates. After annealing at 723 K for 3 h, both {0002}<1-010> and {1-010}<1-120> components are strengthened moderately. This indicates that grains with both two components mentioned above grow faster than those with other orientations. The {1-010}<1-120> component disappears and the intensity of {0002}<1-010> component decreases significantly after hot rolling with a 30% reduction at 623 K. This is mainly attributed to rotational dynamic recrystallization (RDX) during the hot rolling.     

AZ31B镁合金板材快速气压胀形行为

对板厚1.0 mm的细晶AZ31B镁合金板材进行快速气压胀形研究,在300~400℃的温度范围内进行了各种气压下300 s的快速气压胀形试验,研究温度和气压对AZ31B板材快速气压胀形能力的影响。结果表明:在不同温度下,胀形高度均随着气压的升高而增大,但气压升高到一定程度时,胀形时间不到300 s即产生破裂;胀形高度在胀形温度400℃时出现峰值为45 mm。在400℃和0.6 MPa条件下,胀形5 min时相对胀形高度达到1.13。胀形件壁厚分布不均匀,温度越高,壁厚分布不均匀度越高。最后,研究了不同温度下快速气压胀形时胀形件微观组织的演变规律。     

不同加载路径下的AZ31B镁合金的成形极限

为了分析实际成形过程中AZ31B镁合金产生破裂的原因,并为改善工艺条件提供实用可靠的判据,采用实验和有限元模拟相结合的方法研究AZ31B镁合金的成形极限.分别对沿轧制方向、垂直于轧制方向、与轧制方向成45°的3种方向的试件进行单向拉伸实验,获得AZ31B镁合金的工程应力-工程应变曲线,获得材料的真实应力-真实应变曲线和...