Annealing behaviour of Mg-3Al-1Zn alloy sheet obtained by a combination of high-temperature rolling and subsequent warm rolling

The recrystallization and grain growth behaviour of Mg-3Al-1Zn alloy sheets with a deformation microstructure, obtained by a combination of high-temperature rolling and subsequent warm rolling, was investigated at different stages of annealing. The basal texture was significantly weakened as a result of the formation of new grains with a largely altered c-axis orientation relative to the initial basal orientation owing to discontinuous static recrystallization during primary recrystallization. The new grains nucleated mostly at the pre-existing grain boundaries rather than at the intersections of twins or within the twins. Subsequent grain growth led to further progression of the texture weakening accompanied by an enhancement in the basal pole inclination.     

Effect of speed-ratio on microstructure, and mechanical properties of Mg-3Al-1Zn alloy, in differential speed rolling

The effect of speed ratio (SR) in differential speed rolling on the development of texture and microstructure in Mg-3Al-1Zn alloy was systematically investigated in a wide SR range between 1 and 3 at a fixed thickness reduction of 20%. At low SRs, deformation bands and shear bands were dominant. At high SRs ≥ 2, however, dynamically recrystallized microstructures were developed. The intensity of the basal texture component increased with SR, but decreased to the level of the starting material at high SRs ≥ 2. The occurrence of the dynamic recrystallization at high SRs was attributed to high-dislocation density accumulation and high temperature rise of a deforming sheet due to large plastic deformation of which amount increased with SR. The basal texture weakening at high SRs was attributed to extensive tension twinning that occurred in the basal-oriented matrix, which is rarely observed in conventional rolling. Due to the positive effect of texture and microstructure, tensile ductility improvement was significant as compared to that by symmetric rolling.     

Improvement of formability of Mg–Al–Zn alloy sheet at low temperatures using differential speed rolling

The differential speed rolling (DSR) with a roll speed ratio of 1.167 was carried out on an AZ31B magnesium alloy in order to investigate its effects on the formability. Compared with the normal rolled sheet exhibiting approximately the same average grain size, the Erichsen values of the DSR processed sheet with an inclination of basal pole in the rolling direction significantly increased by about 1.5 and 1.9 times at room temperature and at 423 K, respectively. The deep-drawing temperature limit for a drawing ratio of 1.5 was also lowered from 443 K to 423 K. The improvement of the press formability at low temperatures can be attributed to the texture modifications, which led to a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent.     

Cold stamping formability of AZ31B magnesium alloy sheet undergoing repeated unidirectional bending process

The repeated unidirectional bending (RUB) process was carried out on an AZ31B magnesium alloy in order to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of the RUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach 1.5 at room temperature. It was also confirmed that cell phone housings can be stamped successfully in crank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stamping formability at room temperature can be attributed to the texture modifications, which led to a lower yield strength, a larger fracture elongation, a smaller Lankford value (r-value) and a larger strain hardening exponent (n-value).     

铝合金板材温热成形性能

在20℃～300℃的温度范围内,分别对7B04-T6和6061-T6铝合金薄板进行了单拉试验,结果表明,7B04-T6高强度铝合金的断后延伸率和拉伸极限应变在温热状态下都有显著的提高,比较适合于温热成形,而6061-T6则不太适合。另外,基于Fields&Backofen本构方程,对7B04-T6在不同温度状态下的强化规律进行了分析和探讨,结果表明,随着温度的逐渐升高,应变强化指数n值不断减小,应变率敏感系数m值则显著增大,应变率强化明显增强,这也是在温热状态下其成形性能提高的主要原因。     

Influence of yttrium on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy

The influence of Y on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy was investigated. The results show that the phase compositions of Mg-5Li-3Al-2Zn consist of α-Mg and AlLi phases. Adding Y to the alloy results in the formation of Al₂Y compound and facilitates grain refinement. The addition of 0.8 wt.% Y produces the smallest grain size. The tensile tests performed at room temperature show that the additions of Y can improve the mechanical properties of the alloy; the tensile strength and ductility reach peak values when the Y additions are 0.8 wt.% and 1.2 wt.%, respectively. The mechanisms of improvement are related to grain refinement and compound strengthening effects.     

Influence of Continuous Bending Process on Texture Evolution and Mechanical Properties of AZ31 Magnesium Alloy

Mg–3Al–1Zn alloy sheets have been deformed by continuous bending(CB) to investigate the effects of pro cessing parameters(bending angle and repetitive passes) on the texture and formability. The samples exhibited a bimoda microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing. The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD, and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing Compared with the as-received sample, the yield strength of CBA-120-2 sample significantly decreased from 183 to112 MPa, and a smaller r-value and a larger n-value were obtained. The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm, increased by about 135%. The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.     

Effect of temperature,strain rate and fibre orientation on the plastic flow behaviour and formability of AZ31 magnesium alloy

The sheet formability of AZ31 magnesium alloy has been widely investigated by means of uniaxial tensile and hemispherical punch tests, performed at different temperatures and strain rates, using samples with different fibre orientations. The results of the uniaxial tensile tests were analysed in terms of flow curves, ductility and microstructural evolution. They show that the flow stress decreases and ductility increases as temperature rises and strain rate reduces; the ductility is almost independent of the fibre orientation that, however, slightly affects the flow stress values. The formability, described by the forming limit curves (FLCs), improves with increasing temperature and decreasing strain rate. Moreover, formability along the rolling direction (RD) is higher than that along the transversal one (TD), even if the FLCs obtained along the TD have a larger extension in the drawing side than the ones along the RD. Such behaviours were related to the constitutive parameters and microstructure developed during deformation.     

AZ31镁合金薄板经不同累积应变的连续弯曲变形后的显微组织与成形性能

对AZ31镁合金板材进行不同累积应变的连续弯曲变形及退火处理,随后对显微组织与力学性能的变化进行了研究。结果表明:经不同累积应变的连续弯曲变形后,镁合金板材的显微组织中没有发现孪晶,退火后,板材表层的晶粒异常长大,粗晶层的厚度随着累积应变的增加而增加,并且镁合金板材的织构朝RD方向偏转,偏转角度随累积应变的增加而增大;与原始板材相比,连续弯曲变形及退火处理使镁合金板材呈现出较好的室温成形性能(杯突值由2.3 mm提高到4.9 mm,提高了~113%),这主要归因于基面织构的改善使镁合金板材的r值减小与n值增大。     

Mg-9.5Li-2.56Al-2.58Zn合金组织及室温变形行为

以Mg-9.5Li-2.56Al-2.58Zn合金为对象,研究其组织形貌及相组成.并利用UTM5305电子万能试验机对其进行了不同应变速率以及不同变形量的室温压缩实验,获得真应力-应变曲线,构建合金的室温变形本构方程.研究压缩前后合金的微观组织和压缩性能演变规律.结果 表明,Mg-9.5Li-2.56Al-2.58Zn...     

Effect of high density electropulsing treatment on formability of TC4 titanium alloy sheet

An annealed TC4 titanium alloy sheet was treated by high density electropulsing(Jmax=(5.09-5.26)×103A/mm2,tp=110μs)under ambient conditions.The effect of electropulsing treatment(EPT)on the plastic deformation behavior of TC4 titanium alloysheet was studied using uniaxial tension tests.The experimental results indicate that electropulsing treatment significantly changesthe mechanical properties of sheet metal:the uniform elongation is increased by 35%,the yield stress is decreased by 19.8%and theyield to tensile ratio is decreased by 17.6%.It is of significant meaning to improve the formability of TC4 titanium alloy sheet.Theoptical microscope and scanning electron microscope(SEM)were used to examine the changes of the microstructure and the fracturemorphology before and after the electropulsing treatment.It is found that recrystallization occurs in the sheet metal and dimples infracture surface are large and deep after the electropulsing treatment.The research results show that the electropulsing treatment is aneffective method to improve the formability of titanium alloy sheets.     

Influence of trace Ca addition on texture and stretch formability of AM50 magnesium alloy sheet

The AM50, AM50–0.1Ca, AM50–0.3Ca and AM50–0.5Ca (wt.%) alloys were hot-rolled and their mechanical properties were determined for the purpose of investigating the effect of trace Ca addition on the texture and stretch formability of AM50 alloy. The results show that the addition of trace Ca can effectively modify the basal texture, which is characterized by the split of basal poles deviated from the normal direction (ND) after the hot rolling, while a broad spread of the basal planes toward the transverse direction (TD) after the annealing. Such change of the basal texture is related to the prior formation of massive compression twins and the decrease of the c/a ratio. Erichsen value increases from 2.25 to 4.21 mm with the increase of Ca content. The enhancement of stretch formability is ascribed to the weakened basal texture, which results in the increase of n-value and the decrease of r-value.     

Grain refinement and plastic formability of Mg-14Li-1Al alloy

Al-5Ti-1B master alloy was added into Mg-14Li-1Al(LA141)alloy and then LA141 sheets were prepared by extrusion and cold rolling.The effect of the addition level of Al-5Ti-1B master alloy on the grain size of LA141 alloy was investigated as well as the effects of the total reduction of cold rolling and the annealing temperature on microstructure,mechanical properties and plastic formability of the LA141 sheets.The results show that the optimal addition level of Al-5Ti-1B master alloy into LA141 alloy is 1.25%(mass fraction)and LA141 alloy has the finest grains.With the increase of the total reduction of cold rolling,the grains of the as-rolled LA141 sheets were flattened gradually.A proper anneal temperature of 200℃ is obtained for the cold rolled LA141 sheets. Under this condition,microstructure of the LA141 sheets consists of fine and uniform equiaxed grains and has higher Erichsen cupping index(IE).     

热处理对铸造Mg-4Y-3Nd-1.5Al合金显微组织和力学性能影响

本文通过显微组织分析和力学性能测试等试验手段，研究了热处理对Mg-4Y-3Nd-1.5Al合金显微组织和力学性能的影响。结果表明:铸态合金组织中第二相主要为Mg5RE、Mg24RE5和Al2RE相，经固溶处理后（525℃×6h+550℃×12h），Mg5RE、Mg24RE5相完全溶解，Al2RE不发生溶解。Mg-4Y-3Nd-1.5Al合金具有明显的时效硬化行为，经固溶+时效处理后，合金的力学性能显著提高。经固溶（525℃×6h+550℃×12h）+峰时效（225℃×10h）处理后，Mg-4Y-3Nd-1.5Al合金屈服强度、抗拉强度和延伸率分别为:185MPa、262MPa和6.5%。获得良好的力学性能与合金中析出高密度的细小β""和β"相有关。     

织构对基于Mg-3Al-1Zn合金的镁空气电池性能的影响

在本论文中,商用AZ31镁合金板材被用为实验材料。为了研究织构对镁空气电池性能的影响,分别制备了基于板材轧面和截面的镁空气电池。与已经报道过的关于织构对镁合金电化学性能的影响的研究不同,本文所用实验材料的表面粗糙度与实际应用中镁合金板材的表面粗糙度相似。通过电化学阻抗谱研究了试样的电化学性能,结果表明轧面比截面更耐腐蚀。通过恒流放电测试研究了电池的放电性能,结果表明基于截面阳极的镁空气电池和基于轧面阳极的镁空气电池相比具有更高的阳极效率（两种电池的阳极效率分别为71.3%和65.7%）。放电24小时之后,通过扫描电子显微镜研究了镁合金阳极基体的表面形貌。轧面阳极显示出一个具有更多孔洞和沟壑的阳极表面,这可能是导致它具有低阳极利用率的原因。因此,被(10-10)、 (11-20) 和(10-11)取向晶粒所主导的轧面阳极更合适于被运用于镁空气电池。     

Improving single pass reduction during cold rolling by controlling initial texture of AZ31 magnesium alloy sheet

The AZ31 magnesium alloy sheets obtained by multi-pass hot rolling were applied to cold rolling and the maximum single pass cold rolling reduction prior to failure of AZ31 magnesium alloy was enhanced to 41%. Larger single pass rolling reduction led to weaker texture during the multi-pass hot rolling procedure. The sheet obtained showed weak basal texture, while the value was only 1/3–1/2 that of general as-rolled AZ31 Mg alloy sheets. It was beneficial for the enhancement of further cold rolling formability despite of the coarser grain size. The deformation mechanism for the formation of texture in AZ31 magnesium alloy sheet was also analyzed in detail.     

Effect of vertical rolling at various temperatures on subsequent multi-pass severe rolling of AZ31B alloy sheet

AZ31B alloy was subjected to vertical rolling at various temperatures prior to multi-pass severe rolling processing including initial rolling including one 80% reduction pass and finish rolling at 300 °C and 350 °C, respectively. The depth and number of edge crack, microstructure evolution and tensile properties were examined. The results indicate that pre-vertical rolling at low temperature before severe rolling can significantly restrain edge crack, change relative frequency distribution of edge-crack depth, increase microstructure homogeneity and sharply change the intensity and distribution of basal texture of initial-rolled sheets. The level of edge crack increases with increased vertical rolling temperature above 100 °C mostly due to the combination of shear band density, microstructure homogeneity, grain size and texture of rolled sheets. Compared with conventional rolling, the effect of vertical rolling on final mechanical properties depends on the finish rolling temperature due to the combination of shear bands, twins and grain size. The variation trend of mechanical properties with increased vertical rolling temperature is also sensitive to finish rolling temperature. For as-rolled sheets, the severe rolling route with vertical rolling at 100 °C and finish rolling at 300 °C should be required.