稀土La对半固态A356初生相细化机制的研究

利用Al-La稀土中间合金对液态A356铝合金进行了细化处理,并用低过热度浇注技术制备了半固态A356铝合金浆料,研究了稀土La对所制备半固态A356铝合金的初生α相形貌和尺寸的影响.研究结果表明,含有适量稀土La的A356铝合金经低过热度浇注可制备具有颗粒状和蔷薇状初生α相的半固态浆料,稀土La可显著改善半固态A356铝合金中初生α相的晶粒尺寸和颗粒形貌.稀土La对半固态A356铝合金的初生α相细化机理可能与稀土在铝合金中诱发的共晶反应有关.     

稀土La对半固态A356初生α相细化机制的研究

利用Al-La稀土中间合金对液态A356铝合金进行了细化处理,并用低过热度浇注技术制备了半固态A356铝合金浆料,研究了稀土La对所制备半固态A356铝合金的初生α相形貌和尺寸的影响.研究结果表明,舍有适量稀土La的A356铝合金经低过热度浇注可制备具有颗粒状和蔷薇状初生α相的半固态浆料,稀土La可显著改善半固态A35...     

稀土Y在电磁搅拌条件下对半固态ZL101铝合金初生α相的影响

选用稀土Y 作为ZL101 铝合金的细化剂,同时结合自制变频控制的电磁搅拌设备对合金进行短时弱电磁搅拌,探讨了稀土细化半固态合金的机制和不同电磁搅拌频率,对半固态ZL101-Y 铝合金凝固组织中不同区域的初生α 相的影响及最佳的电磁搅拌频率参数.研究表明:液态ZL101-Y合金经620 ℃低过热度浇注,并在频率为30 Hz 的条件下搅拌15 s,于590 ℃保温5 min 后,其初生α 相的形貌和尺寸达到最佳,其中心部晶粒平均等积圆直径为64.95 μm,平均形状因子为0.80,而边缘晶粒的平均等积圆直径为58.97 μm,平均形状因子达到0.83.在此条件下,半固态ZL101 合金浆料的初生α 相形貌及尺寸好且沿径向分布较均匀.      

半固态A356合金重熔加热时初生相的组织演变

利用低过热度浇注技术制备了半固态A356铝合金坯料,研究了半固态温度区间重熔加热时半固态A356铝合金坯料的初生相形貌的转变过程.结果表明,在半固态两相区保温,半固态A356合金的初生相逐渐团球化,该过程随保温温度的升高而加快.半固态A356铝合金晶粒的圆度与保温温度和保温时间的关系不大,但晶粒的尺寸随着保温温度和保温时间的增加而增大.半固态A356合金试样重熔加热最佳工艺制度为583℃下保温30min,其晶粒平均等积圆直径为80μm,晶粒平均圆度为0.83.     

半固态A356合金重熔加热时初生相的组织演变

利用低过热度浇注技术制备了半固态A356铝合金坯料,研究了半固态温度区间重熔加热时半固态A356铝合金坯料的初生相形貌的转变过程.结果表明,在半固态两相区保温,半固态A356合金的初生相逐渐团球化,该过程随保温温度的升高而加快.半固态A356铝合金晶粒的圆度与保温温度和保温时间的关系不大,但晶粒的尺寸随着保温温度和保温时间的增加而增大.半固态A356合金试样重熔加热最佳工艺制度为583℃下保温30min,其晶粒平均等积圆直径为80μm,晶粒平均圆度为0.83.     

立弯式浇道对半固态A356铝合金浆料组织的影响

采用立弯式浇道制备A356铝合金半固态浆料,研究了浇注温度对A356铝合金半固态浆料组织的影响,并考察了浆料经过均热处理后的组织。结果表明,采用立弯式浇道可以制备出半固态浆料,在本实验条件下,获得理想的半固态A356铝合金浆料的浇注温度为630℃和640℃,而且随着浇注温度的降低,初生相的形态由树枝状→蔷薇状→颗粒状转变;经过感应均热后,初生相更圆整,且尺寸、分布都很均匀。     

浇注温度对合金熔体冷却规律和半固态组织的影响

介绍了一种实验室自主研发的轻合金半固态浆料制备设备——锥桶式流变成形机(TBR),该设备利用刻有凸纹和沟槽的内、外锥桶的相对转动,使合金熔体在凝固过程中受到剧烈的剪切搅拌,从而获得合金半固态浆料.对TBR工艺的传热模型进行了推导,以A356为实验材料得出制备的A356铝合金半固态浆料温度与浇注温度的关系式,同时分析了不同浇注温度下合金熔体的冷却规律和获得的半固态组织形貌.结果表明,适当降低A356合金熔体的浇注温度可以延长初生固相受到的剪切时间和增加剪切次数,从而获得细小、均匀的半固态组织.当浇注温度为640℃时,初生固相平均晶粒尺寸为68μm,形状因子为0.82.     

超声振动对半固态ZL101-La合金初生相的影响

利用超声振动技术制备了半固态ZL101-La合金浆料,研究了超声振动工艺参数,如：超声功率、超声导入温度和超声处理时间对半固态ZL101-La合金初生相的影响.结果表明：利用超声振动和稀土复合制备半固态ZL101合金浆料是可行的,超声功率是影响初生相形貌的主要因素.通过正交实验设计获得了超声振动场下制备半固态ZL101-La铝合金浆料的合适工艺方案,即：超声功率为150 W,超声导入温度为650℃,超声作用时间为30 s.     

双向间歇电磁搅拌对半固态A356-Ce合金凝固组织的影响

利用强剪切强对流的双向间歇电磁搅拌技术与低过热度浇注技术复合工艺作用合金熔体,制备了凝固显微组织形貌为晶粒尺寸细小、形态规则圆整的半固态A356-Ce合金铸锭,研究了在磁场作用时间恒定15 s时铝合金熔体施加不同磁场频率、间歇时间对合金中初生α相晶粒尺寸和形貌演变方式的影响规律。结果表明,在合理的试验磁场频率和间歇时间范围内,随着磁场频率和间歇时间增加,初生相的尺寸逐渐细化、圆整度和分布均匀性增大。在磁场频率30 Hz、间歇时间3 s电磁搅拌工艺条件下半固态初生相的晶粒尺寸细化和球化程度达到最佳,组织中初生晶粒均匀分布,初生相的形貌由初始发达粗大的树枝晶向细小圆整的球状非枝晶转变,其平均等积圆直径处于各磁场频率和间歇时间作用下的最小值35.2μm;平均形状因子达到了峰值0.81。采用该复合工艺可制备出满足流变成形需要的优质的流变浆料。     

Ce对A356合金的影响及细化机制的研究

研究了Ce对A356铝合金晶粒细化的效果以及对其力学性能的影响。结果表明:在未添加稀土Ce时,A356铝合金结晶时,其中的初生相α-Al呈现为粗大的树枝状。在添加不同量的稀土Ce时,A356铝合金中的初生相α-Al明显得到细化,树枝状晶转化为等轴晶。在Ce合金添加量为0. 1%时其细化效果最好,α-Al的等效直径和形状因子均达到最优水平,分别为24. 5μm和0. 61;二次枝晶臂间距最小,平均二次枝晶臂间距为14. 63μm;其力学性能也达到最佳,抗拉强度和延伸率分别为165. 89 MPa和3. 5%,合金的硬度为HV 77. 6。添加量超过0. 1%时,其细化效果会随着添加量的增加而逐渐减弱。稀土Ce对于合金晶粒细化比较符合异质形核理论,Al-Ce中间合金中的Al11Ce3和α-Al具有相似的晶体结构,而且晶格常数也能与之相对应。在A356合金液中添加Al-Ce中间合金时,Al11Ce3粒子作为A356合金凝固时的异质形核点从而促进细化。     

Microstructure and rheological properties of a semisolid A356 alloy with erbium addition

The effects of erbium addition on the rheological properties and microstructure of a semisolid A356 alloy were studied. The semisolid slurries were prepared through the serpentine channel technique before they were thixoformed using parallel-plate compression with cylindrical discs. The grain and globule size decreases as the Er content increases, resulting in an improved and uniform distribution of spherical primary α-Al phase within the semisolid slurry. The addition of the Er modifies the grain morphology and size of the α-Al grains, resulting in a better and more uniform distribution of spherical primary α-Al phase within the semisolid slurry. As a result, rheocast quality index increases with the addition of Er, which is suitable for the thixoforming process. The A356 alloy without Er has the highest viscosity herein. The viscosity decreases, and the flow characteristics of the semisolid feedstock are expected to improve when Er is added as a result of the refinement of primary α-Al and modification of eutectic silicon. Furthermore, the refined semisolid A356 alloys with Er show a slightly larger fraction of high-angle grain boundaries compared to that for the unre?ned alloy.     

Microstructural and Statistical Study of Semisolid Casting of 6061 Alloy Using a Miniature Cooling Slope

Preparation of metallic semisolid slurries using the cooling slope method is increasingly becoming popular because of the simplicity of design and control of the process. Microstructural features of the resultant semisolid castings such as size and sphericity of the primary particles are affected by several processing parameters such as pouring rate, cooling slope surface angle and length as well as the melt superheat. In this work, a miniature cooling slope for semisolid casting of small parts was built and attempts were made to develop an empirical relationship showing the correlation between the sphericity of the microstructure of semisolid cast 6061-aluminum alloy and the processing variables. The relationships were developed by a two-level factorial method. The results showed that the interaction of cooling slope length and pouring rate factors had the most effect on the sphericity of the final semisolid cast microstructure.     

Investigation of spherisation in microstructures of aluminium casting alloys for thixoforging process

Thixoforging combined with low superheat casting (LSC) is a promising shaping process for aluminium casting alloys. LSC process is based on rapid solidification of an alloy which cast with low pouring temperature. With this method, a feedstock material is produced with non-dendritic microstructure that ready for spherisation in reheating sequence of further semi-solid process. Al-Si alloys are still castable even at low temperatures due to their excellent fluidities. This study subjects to present spherisation of A356 and A380 alloy billets cast with LSC process that provides appropriate beginning material with relatively high sphericity. Obtained billet parts were reheated for different times at a semi-solid state temperature. Some of these billets were directly quenched for observing the effects of reheating and the others were thixoforged. With sufficient reheating time, deformation of thixoforging process did not significantly affect on the spherical microstructure. Unnecessarily long reheating period caused excessive grain growth. A356 alloy had higher spherisation tendency than A380 alloy under similar process conditions.     

Mechanical properties of the A356 aluminum alloy modified with La/Ce

The research of rare earths for the synthesis of materials with improved mechanical performance is of great interest when they are considered for potential applications in the automotive industry. In this regard, the effect on the mechanical properties and microstructure of the automotive A356 aluminum alloy reinforced with 0.2 (wt.%) Al-6Ce-3La (ACL) was investigated. The ACL was added to the melted A356 alloy in the as-received condition and processed by mechanical milling. In the second route, the effect of the ACL processed by mechanical milling and powder metallurgy techniques was investigated, and compared with the results obtained from the A356 alloy strengthened with ACL in the as-received condition. Microstructural properties were evaluated by means of X-ray diffraction in order to observe the solubility of Ce/La in the Al matrix. In addition, electron microscopy was employed in order to investigate the effect of milling time on the size and morphology of La/Ce phase under milling process. Mechanical properties of the A356 alloy modified with ACL were measured by hardness and tensile test. For comparison unmodified specimens of the A356 were characterized according to the previous procedure. The microstructural and mechanical characterization was carried out in specimens after solution and artificial aging. Observations in scanning electron microscopy indicated a homogeneous dispersion of La/Ce phases by using both routes; however, mechanical results, in the modified A356 alloy with the ACL in the as-received condition, showed an improvement in the mechanical performance of the A356 alloy over that reinforced with the ACL mechanically milled.     

稀土细化剂对半固态A356铝合金等温热处理组织的影响

利用低温浇注与晶粒细化法制备了半固态A356铝合金坯料,研究了在细化剂作用下等温热处理工艺条件对其组织的影响规律.研究结果表明,稀土细化剂的加入对试样等温热处理前的铸态组织和热处理后的加热组织都有明显的改善作用,且稀土细化及低温浇注共同作用时,所获得的半固态非枝晶A356铝合金试样等温热处理最佳工艺条件为583℃下保温30 min,此时坯料触变性良好,其晶粒平均圆度达到0.83,晶粒平均等积圆直径达到80μm.     

Scaling Analysis of Solidification of Liquid Aluminum Alloy Flowing on Cooling Slope

Among all methods of metal alloy slurry preparation, the cooling slope method is the simplest in terms of design and process control. The method involves pouring of the melt from top, down an oblique and channel shaped plate cooled from bottom by counter flowing water. The melt, while flowing down, partially solidifies and forms columnar dendrites on plate wall. These dendrites are broken into equiaxed grains and are washed away with melt. The melt, together with the equiaxed grains, forms semisolid slurry collected at the slope exit and cast into billets having non-dendritic microstructure. The final microstructure depends on several process parameters such as slope angle, slope length, pouring superheat, and cooling rate. The present work involves scaling analysis of conservation equations of momentum, energy and species for the melt flow down a cooling slope. The main purpose of the scaling analysis is to obtain a physical insight into the role and relative importance of each parameter in influencing the final microstructure. For assessing the scaling analysis, the trends predicted by scaling are compared against corresponding numerical results using an enthalpy based solidification model with incorporation of solid phase movement.