变质和铸造工艺对Al-20Si合金初生Si组织的影响

研究了铸造工艺和变质处理对Al-20Si合金中初生Si组织的影响。利用光学显微镜以及Image Pro金相分析软件,对经过不同铸造工艺和变质处理的过共晶Al-Si合金组织进行了观察、分析和计算。结果表明,控制浇注温度、铸型温度以及变质剂加入量可细化初生Si颗粒,且变质剂细化初生Si颗粒的效果远大于浇注温度、铸型温度;当浇注温度为760℃或铸型温度为200℃时,凝固组织中的初生Si颗粒尺寸小于90μm,而磷盐变质剂加入量为0.8%或Cu-14P中间合金加入量为0.4%时,初生Si颗粒尺寸小于20μm。     

变质工艺对过共晶Al-Si合金连铸坯组织的影响

采用美国标准TP-1模具及模拟方法,研究了Al-Si-P变质剂的加入量、熔体浇注温度以及变质保温时间对过共晶Al-Si合金连铸坯料凝固组织的影响规律.结果表明,Al-Si-P变质剂加入量(超过0.02%)和变质保温时间对合金显微组织细化的影响不明显;而浇注温度对初生Si的大小分布影响较大,浇注温度越高,初生Si越细小、分布也越均匀.在合适的工艺匹配条件下,可以获得初生Si细小、形貌较为规则圆整、分布均匀的显微组织.     

Al-8Ti-2C对Al-P中间合金变质效果的促进作用

研究了自制Al-P中间合金对共晶及过共晶Al-Si的变质作用，发现该Al-P中间合金对共晶及过共晶Al-Si合金都具有优良的变质效果。同时还发现，当铝合金熔体中加入Al-8Ti-2C中间合金时，Al-P中间合金对两类Al-Si合金的变质效果会增强。当Al-24Si合金中TiC含量为0．03％(以Al-8Ti-2C中间合金方式)时，初晶Si的平均尺寸由原来的47μm细化为41μm，最大尺寸由原来的75μm降为55μm；加入Al-P中间合金和TiC颗粒50min后，就可以出现变质效果，时间再延长，变质效果也不会有更大的提高。当Al-12Si合金中TiC含量为0．03％时，初晶Si的平均尺寸由原来的50μm变为30μm。     

浇注温度对Mg2Si增强过共晶Al-Si合金组织与性能的影响

采用液态熔融法制备Mg2Si增强过共晶Al-Si合金自生复合材料，研究了浇注温度、稀土（Pr）变质处理对铸造显微组织与性能的影响。结果表明，在液相线附近，浇注温度为720℃时，晶粒均匀细小；Pr变质剂对初生硅及共晶组织均有明显的细化效果，并细化Mg2Si、改变其形貌与尺寸，可显著提高合金的力学性能。     

Sr/P变质处理对挤压铸造Al-17.5Si合金组织与性能的影响

研究Sr和P变质对挤压铸造Al-17.5Si合金组织与力学性能的影响。试验结果显示:挤压铸造对过共晶Al-17.5Si合金的组织产生了显著的影响,共晶组织明显细化,初生Si相的数量减少并细化,同时力学性能显著提高。Sr变质后的Al-17.5Si合金在压力下凝固,共晶Si相进一步细化,变为十分细小的纤维状,合金的抗拉强度和伸长率比重力铸造分别提高了59%和328.7%。当P变质处理Al-17.5Si合金挤压铸造成形后,合金组织中却出现了大量的粗大初生Si相颗粒,使得合金的力学性能呈现了降低的趋势。由此确定,挤压铸造过共晶Al-Si合金的最佳变质处理为Sr变质,P变质不适用于挤压铸造成形的过共晶Al-Si合金。     

压铸条件下过共晶铝硅合金P变质的必要性

在铝合金压铸生产过程中,Al-P中间合金变质处理和压力铸造工艺都能够使过共晶铝硅合金中的初晶硅晶粒细化.探讨Al-P中间合金变质处理,分别在压铸工艺条件下和普通金属型条件下,对过共晶Al-15Si合金组织的不同影响.试验表明,压铸条件下未经Al-P变质的和经Al-P变质的Al-15Si合金与金属型条件下未经Al-P变质的Al-15Si相比,初晶Si尺寸分别减小50%和75%左右;在相同的压铸工艺条件下,Al-P变质后Al-15Si合金初晶Si尺寸,比未经过Al-P变质的Al-15Si合金初晶Si尺寸减小40%左右.论证了在Al-Si系过共晶铝合金压铸件生产过程中,Al-P中间合金进行变质处理的必要性.     

变质工艺对亚共晶Al-Si合金共晶硅细化的影响

研究了工业生产Sr变质亚共晶Al-7%Si合金时,变质剂含量、变质温度、变质时间、浇注温度等工艺参数对合金共晶硅细化及其性能的影响。结果表明,在大规模工业化生产中,上述工艺参数严重影响共晶硅的变质效果。采用Al-10%Sr对亚共晶Al-7%Si合金进行变质,在w(Sr)=0.015%时,保温40min后,共晶团内的Si完全成为圆颗粒状,尺寸为5～10μm,达到最佳变质效果。采用Sr变质亚共晶Al-7%Si合金最佳变质温度为700℃,变质后共晶硅组织分布均匀;浇注温度为640℃时的铸件宏观组织最佳,晶粒度可稳定的达到2级,升高浇注温度,晶粒度提高。精炼后,变质时间为30～60min进行浇注,试样针孔度最小,熔体洁净程度高。     

Al-Ba中间合金及其对共晶Al-Si合金的变质处理

制备出一种新型的Al-Ba中间合金变质剂，并探讨了它对Al-Si合金的变质处理效果。试验结果表明，Al-Ba中间合金对共晶Si的变质效果与Al-Si合金相当，可以使共晶Si由片状变为珊瑚状，显著改善Al-Si合金的显微组织。另外，用Al-Ba中间合金与A1-P中间合金同时对Al-Si合金进行变质处理时，还可达到双重变质效果。同时，用Al-Ba中间合金时，变质持效时间比钠盐变质剂更长久，显示出较好的应用前景。     

电磁搅拌与变质复合作用对Al-20Si合金初生硅相的影响

使用电磁搅拌、变质处理及其复合工艺分别成功制备了过共晶Al-20Si半固态浆料，研究了电磁搅拌和变质的复合作用对过共晶Al-20Si合金中初生Si长大和形貌的影响。研究结果表明：复合作用可以获得比单种变质处理和电磁搅拌的过共晶Al-20Si合金更加细小、更加圆整的初生Si组织。复合作用获得的初生硅比单一处理尺寸平均减小25．19％，圆整度平均提高8．40％。而且共晶Si组织也得到球化。复合作用细化组织的机理为：变质后施加旋转磁场，促进了变质剂的扩散，更多的初生Si与共晶Si组织相互打碎，深化了变质和电磁搅拌效果，细化显微组织。     

压铸条件下过共晶铝硅合金P变质的必要性

在铝合金铸件生产过程中,Al-P中间合金变质处理和压力铸造工艺都能够使过共晶铝硅合金中的初晶硅晶粒细化.探讨Al-P中间合金变质处理,分别在压铸工艺条件下和普通金属型条件下,对过共晶Al-15Si合金组织的不同影响.试验表明:与金属型条件下未经过Al-P变质的Al-15Si合金组织相比:压铸工艺条件下未经过Al-P变质的合金,初晶Si尺寸减小50%左右;同一压铸工艺条件下经过Al-P变质后的合金,初晶Si尺寸减小75%以上.在相同的压铸工艺条件下,Al-P变质后Al-15Si合金初晶Si尺寸,比未经过Al-P变质的Al-15Si合金初晶Si尺寸减小40%左右.论证了在Al-Si系过共晶铝合金压铸件生产过程中,Al-P中间合金进行变质处理的必要性.     

原位观察共晶硅对Al-20%Si合金裂纹形成与扩展的影响

采用共聚焦激光扫描显微镜原位观察了Al-20%Si合金在拉伸过程中裂纹形成与扩展过程,研究了共晶硅对Al-20%Si合金裂纹形成、扩展的影响。结果发现:随固溶温度升高,Al-20%Si合金共晶硅粒化效果显著。铸态Al-20%Si合金拉伸过程中在针状共晶硅处容易产生裂纹,且裂纹主要在共晶硅之间扩展。经560 ℃固溶6 h,190 ℃时效10 h后,合金中针状共晶硅完全转变为颗粒状,有效降低了裂纹扩展速度,合金的抗拉强度和塑性明显提高。     

Sr,B添加对Al-15.5%Si合金中共晶团尺寸的影响

考察了Sr，B及Sr＋B联合作用对Al-15．5％Si（质量分数）合金中共晶团尺寸大小的影响．实验结果表明，随合金中Sr量增加，共晶团尺寸呈减少的趋势，冷却速度对共晶团的影响也很显著；在Sr变质的合金中加入B，共晶团尺寸先显著下降，随B量增加降低幅度趋于平缓；在未变质的Al-15.5％Si合金中单独加B，共晶硅由粗大的片状变为细长的层片状，层片间距明显降低．分析认为，合金中加入Sr，导致共晶过冷度增大，因而共晶团形核驱动力增大促使共晶团细化；合金中加入B，增加了共晶团有效形核基底的数量促使共晶团显著细化．     

Microstructure and mechanical properties of hypereutectic Al-Si alloy modified with Cu-P

The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.     

Eutectic nucleation in Al-25wt.%Si alloy through DSC

Eutectic nucleation in hypereutectic Al-25wt.%Si alloy with the addition of P was studied by calculating the activation energy and nucleation work. The results indicate that P refinement, which can decrease the activation energy as well as nucleation work of eutectic solidification, can increase the eutectic nucleation frequency of Al-25wt.%Si alloy, so the addition of P can refine the eutectic structures of hypereutectic Al-Si alloys. According to the calculations, there is a certain relationship between the precipitation of primary silicon and eutectic solidifica-tion, and the eutectic nucleation mode is independent of morphology transition.     

Al—Sr中间合金变质效果的遗传效应

通过不同铸工艺制取的相同成要不同形貌的变质用Ａｌ－８．６２％Ｓｒ中间合金，具有明显的变质效果差异。在砂型条件下，用Ａｌ－８．６２％Ｓｒ中间合金对共晶Ａｌ－Ｓｒ合金进行变质处理，加入使Ａｌ－Ｓｒ合金含０．１％Ｓｒ的锭料和加入使Ａｌ－Ｓｒ合金含０．０５％Ｓｒ的激冷薄片，二者的变质效果相当，都为５级。在金属型条件下，加入使Ａｌ－Ｓｒ合金含０．０６％Ｓｒ锭料和加入使Ａｌ－Ｓｉ合金含０．０３％Ｓｒ的激冷薄片     

Bi对Al-18%Si合金微观组织与力学性能的影响

研究不同的Bi含量对过共晶Al-18%Si合金微观组织与力学性能的影响.试验表明,Al-18%Si-x%Bi(x=1,2,3,4,5)合金中,大部分Bi在基体中以小颗粒状弥散均匀分布,局部出现Bi的聚集;同时,Bi的加入对合金中的共晶硅起到一定的细化作用;随着Bi含量的增加,共晶硅组织由粗大针片状变成短杆状,当Bi含量达到3%时,共晶硅转变为均匀分布于基体的蠕点状,当Bi含量为4%或5%时,共晶硅没有进一步的细化.另外,力学性能和摩擦试验研究发现:Al-18%Si-3%Bi合金的抗拉强度由Al-18%Si合金的168 MPa提高为189 MPa,摩擦系数由0.4372降为0.3879,磨损量仅为不含Bi的20%.     

Effect of phosphorus and heat treatment on microstructure of Al-25%Si alloy

It is known that phosphorus can refine the primary silicon and heat treatment can spheroidize the eutectic silicon. This paper presents an optimal combination of heat treatment processes and P refinement on hypereutectic Al-Si alloy. The optimal P addition amount, and the solution and aging temperatures for Al-25%Si alloy were obtained through the orthogonal experiment, and their modification effects were discussed. The results show that P addition has the greatest modification effect, followed by aging temperature, and the modification effect of solution temperature is the least. The optimized modification parameters are: addition of 0.6% P, solution at 540 oC and aging at 160 oC . In addition, the cooling curve, superheating and hardness of the alloy were also analyzed.     

Study of Melt Thermal-Rate Treatment and Low-Temperature Pouring on Al-15%Si Alloy

Under the condition of melt thermal-rate treatment (MTRT) and low-temperature pouring (LTP), the tensile properties of Al-15%Si alloy are improved, the average size of primary Si is refined to about 20 μm from about 50 μm, and eutectic silicon can be well modified. The ultimate tensile strength and elongation are 201 MPa and 3.5%, and these values increase by 12% and 25%, respectively, compared with that obtained by conventional casting technique. The Al-15%Si alloy modified with Sr and RE additions was also studied for comparison purposes. The tensile properties of the Al-15%Si alloy treated with MTRT + LTP are superior to those modified with Sr or RE addition individually. The eutectic growth temperature difference between modified and unmodified melts was used to indicate the modification level. The modification effect of MTRT + LTP on Al-15%Si alloy is better than that modified with Sr or RE addition.     

Effects of strontium and boron interactions in Al-7Si alloys

Effects of boron and strontium combined treatment on the microstructure of hypoeutectic Al-7Si alloy have been studied.Experimental results show that strontium has no significant effect on the grain refinement efficiency of boron and the eutectic silicon modification efficiency is not only related to the strontium content but also related to the boron content in the Al-7Si alloy melt.There is a negative interaction between boron and strontium that results in the formation of a strontium-boron-aluminum containing compound,which reduces the effective strontium level and decreases the eutectic silicon modification efficiency substantially.The refinement and modification mechanisms remain unchanged after the combined addition of strontium and boron,Based on the experimental results,a model for assessing the modification level in the Al-Si alloy melts after combined addition of boron and strontium was presented.     

MORPHOLOGY OF EUTECTIC Si IN OVER-MODIFIED Al-Si EUTECTIC ALLOY

对高纯的Al-12.5wt-％Si共晶合金中加入金属Na,用扫描电镜和电子探针进行观察分析,结果表明:在共晶成分的Al-Si合金中,随着Na含量的增加,共晶本身会以胞状和树枝状方式构成共晶团。