加热工艺对半固态AlSi7Mg合金的重熔组织的影响

研究了半固态AlSi7Mg合金在不同加热温度制度，不同保温温度，不同保温时间下的显微组织。经电磁搅拌的AlSi7Mg合金在固相线－液相线温度区间保温加热时，共晶相首先熔化，团块状α相逐渐演变成球状。随着保温温度的提高，晶粒形状更圆滑，随保温时间增加，晶粒形状也更圆骨，保温温度太高或保温时间太长时，试样表面有液相析出，靠近表面部位产生大量孔洞，试样在自重作用下变形，随炉加热方式所获得的固相颗粒尺寸比热炉加热方式所获得的固相颗粒尺寸大。     

AlSi7Mg合金坯料在半固态区的结构演化对变形的影响

论述了ＡｌＳｉ７Ｍｇ合金坯料结构演化过程听固相颗粒尺寸及分布、颗粒形貌、颗粒团聚化程度等影响因素,研究了在半固态状态下合金的结构演化对ＡｌＳｉ７Ｍｇ合金变形行为的影响。结果表明,在半固态状态下,亚共晶ＡｌＳｉ７Ｍｇ合金坯料的触变形行为密切依赖于固相的结构和试样在压缩变形前的固相结合演化。初始非枝晶结构或枝晶演化成球状化 很低的应力下变形。在完全球状化条件下,固相颗粒尺寸对应力水平没有明显影响。     

AlSi7Mg合金坯料在固液两相区的初始结构对变形的影响

本文论述了Ａ１Ｓｉ７Ｍｇ合金在半固态下的初始结构对压缩变形行为的影响。结果表明：Ａ１Ｓｉ７Ｍｇ合鑫产的初妈显微结构的固想颗粒尺寸及分布、颗粒形貌、颗粒团聚化程度对兰固态合金坯料的表观粘度有重要的影响。具有初始细昌结构（蔷薇状结构）的合金应力水平较低,具有中等枝晶和粗枝晶结构的合金应力水平较高。非枝晶组织半固态合金变形时固相颗粒变形力的传递数学模型：σｓ＝α２λ１／λ２（Ｔ）ηｆε。     

铝合金半固态加工技术应用

对于垂直式电磁搅拌器 ,提高搅拌效率的最有效措施是减少漏磁通。对于通常的Al Si类合金的半固态加工坯料 ,在足够的搅拌强度下 ,熔体冷却速度控制在 0 .5～ 3.0℃ /s可得到较好的组织。在二次加热时共晶体中的针簇状Si相通过扩散溶解到α相中 ,Si相本身变成细小颗粒 ,初生α相在共晶熔化后才开始球化。对于AlSi9Cu3合金 ,其共晶相在二次加热熔化后重新凝固时 ,Si相呈细小颗粒析出 ;对于A357合金 ,仍然生成针簇状组织。与常规压铸相比 ,半固态压铸内浇道厚度要增加 2～ 3mm ,压射比压要高 5～ 2 0MPa,才能保证充型完好。     

准共晶型ZL109合金半固态锻造成形组织演变特征与力学性能研究

试验研究了ZL109合金在半固态锻造成形过程中（坯料制备，二次重熔和零件成形）的组织演变及成形零件的热处理工艺和力学性能。结果表明：在坯料制备过程中，低过热浇注使坯料微观组织中的共晶硅片细化；在二次重熔时共晶组织熔解，共晶硅片进一步细化和团块化；在半固态锻压成形流动过程中，合金微观组织间发生了摩擦、变形，使得α相球团化，共晶组织细化；半固态锻压零件在热处理过程中，共晶组织中的α相向初生α相聚集成球团状，而共晶组织中的硅颗粒聚集成团块硅相；制备合金坯料的合理低过热浇注温度为566℃，合理的半固态锻造温度为569℃；合金热处理以后伸长率从0％提高到1．42％，比一般铸造方法所得的铸件的塑性明显要高。     

球磨对6061Al合金粉末冷压块在部分重熔过程中组织演变的影响（英文）

研究球磨对6061粉末压块在部分重熔过程中组织演变的影响。结果表明,球磨6061铝合金在部分重熔过程中的组织演变可分为3个阶段:初期共晶相的溶解及其引起的晶粒粗化和长大、初生相颗粒的分离与球状化以及最后颗粒的粗化。与未球磨合金的组织演变相比,球磨使粉末贮存能量,加快了初期演变进程;但大尺寸粉末颗粒的形成使得其后续分离和粗化过程减慢。此外,初始组织越细小、圆整,越有利于得到尺寸较小、更加圆整的半固态组织。适当提高重熔温度有利于获得细小、圆整的半固态组织。     

半固态过共晶Al-Si合金显微组织中近球形α相形成机理的研究

在电磁搅拌法制备的半固态过共晶Ａｌ－Ｓｉ合金的微观组织中发现了大量的近球形α相,实验证明,这种近球形α相是在共晶温度５７５℃以上开始同的。并且在重新加热至固液两相区５７５－５９０℃内保温一段时间后,这种近球形α相仍然存在,理论分析表明,在电磁 电磁搅拌产生的局部微区的高压作用下,过共晶Ａｌ－Ｓｉ合金熔体中Ａｌ原子偏聚团发生合并、长大而形成α相晶核,并且α晶核生长在电磁搅拌的作用下成为近球状。     

多层喷射沉积6066铝合金半固态挤压

采用多层喷射沉积技术制备６０６６铝合金（Ａｌ１．３７Ｓｉ１．３７Ｍｎ０．７７Ｃｕ）锭坯,研究了后续半固态挤压工艺的可行性,及其对材料组织与性能的影响。结果表明,多层喷射沉积６０６６铝合金的平均晶粒度约为１５μｍ,呈等轴晶;在固相线以下退火４０ｍｉｎ后,组织无明显粗化,在半固态发生的晶粒长大符合Ｏｓｔｗａｌｄ晶粒粗化动力学方程,半固态典型组织为球形或近球形的固体颗粒分布于液相中,为适宜于半固态加工的搅溶组织。半固态挤压成形力约为传统热挤压的１／３,挤压件具有良好的第二相粒子分布状态,在Ｔ６热处理过程中组织发生再结晶,晶粒明显细化,二相粒子平均粒度由热挤压态的１μｍ增至２μｍ,体积分数有所增加,材料力学性能达到传统热挤压件水平。     

铸造工艺对AZ91D镁合金半固态组织制备的影响

研究了金属型、湿砂型和干砂型对AZ91D镁合金半固态组织制备的影响.结果表明:增加冷却速率有利于初始凝固组织中存在的非平衡组织的分散细化.原始组织中的非平衡共晶组织在加热过程中大部分扩散溶解而溶入基体中,剩余部分在加热过程中首先熔化.冷却速率越大或预变形处理以后的试样在熔化过程中更容易发生二次枝晶臂之间的合并.提出半固态熔化过程可分为成分均匀化、共晶熔化和部分初生相的熔化和球化完成三个阶段,不同熔化阶段时,控制性因素不同.熔化后的半固态组织中固态颗粒的尺寸和形貌主要与初始组织的形貌、加热过程中非平衡组织的溶解速度及加热速度有关.     

Al-20Si-1Sm合金在半固态等温热处理过程中的组织演变

研究了Al-20Si-1Sm合金在半固态等温热处理过程中的组织演变。结果表明,随着等温热处理温度和时间的增加,液相量增加,共晶α-Al相球化,尺寸先减小后增大。共晶Si呈羽毛状,初生Si裂解成小块状并明显钝化。在等温温度为610℃,保温时间为15min时,合金中共晶α-Al相的球化效果最佳,平均尺寸为37μm,初生Si平均尺寸为30μm。     

Structural evolution of non-dendritic AlSi7Mg alloy during reheating

１　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｔａｌｆｏｒｍｉｎｇｉｎｔｈｅｓｅｍｉｓｏｌｉｄｓｔａｔｅｉｓｎｏｗｂｅｃｏｍｉｎｇａｎｅｗｇｅｎｅｒａｔｉｏｎｍｅｔａｌｆｏｒｍｉｎｇｐｒｏｃｅｓｓｆｏｒｉｔｓｅａｓｙｔｏｒｅａｌｉｚｅｎｅａｒｎｅｔｓｈａｐｅｆｏｒｍｉｎｇ,ｐｒｏｌｏｎｇｅｄｍｏｌｄｌｉｆｅ,ｒｅｄｕｃｔｉｏｎｉｎｓｏｌｉｄｉｆｉｃａｔｉｏｎｓｈｒｉｎｋａｇｅ,ｐｏｒｏｓｉｔｙａｎｄｓｅｇｒｅｇａｔｉｏｎ,ａｓｗｅｌｌａｓｉｔｓｎｏｎｄｅｎｄｒｉｔｉｃｍｉｃｒｏｓｔｒｕｃｔｕｒｅａｎ…     

Effect of vibration frequency on primary phase and properties of grey cast iron fabricated by lost foam casting

The properties of gray cast iron(GCI)are affected by density of matrix,size of flake graphite and primary austenite.In this paper,the Y-type specimen of GCI was prepared by lost foam casting(LFC)with and without vibration,and the influence of vibration frequency on the density of matrix,size of primary phase,and properties of the GCI was studied.The results show that the length of the flake graphite and the size of the primary austenite in GCI firstly decrease and then increase with the increase of the vibration frequency.With a vibration frequency of 35 Hz,the length of the flake graphite is the shortest,the primary austenite is the finest and the density of the matrix is the highest.In addition,the tensile strength,elongation and hardness of the GCI firstly increase and then decrease with the increase of the vibration frequency,due to the refinement of the primary phase and the increase of the matrix density.In order to analyze the refinement mechanism of the primary phase of the GCI fabricated by the LFC with vibration,the solidification temperature fields of the GCI fabricated by the LFC with the vibration frequency of 0 and 35 Hz were measured.The results show that the vibration reduces the eutectic point of the GCI and increases the supercooling degree during the eutectic transformation.As a result,the length of the flake graphite and the size of the primary austenite in GCI fabricated by LFC with the vibration frequency of 35 Hz decrease.     

铸造Al-Si合金Sr变质处理过程中共晶硅形态的渐变行为

通过光学显微镜和SEM考察了共晶硅形态与大小随Al-11.6%Si合金中Sr量的变化.研究发现共晶硅从片状转变成纤维状的过程并不是突变的,而是一个渐变过程,共晶硅的形态存在一个介于二者之间的中间态,具有明显的弯折与分叉,同时也具有纤维硅的特征.随着合金中Sr量的增加,共晶过冷度增大,同时孪晶边界能降低,使得硅相产生弯折、分叉,硅相形态不断向纤维化转变.     

TA15钛合金大型复杂整体构件预锻成形微观组织演化研究

基于DEFORM-3D有限元平台建立了TA15钛合金大型复杂整体构件预锻成形过程的有限元模型,研究了成形参数对预锻成形过程中变形体组织演化和等轴α相晶粒尺寸的影响规律。结果表明:随着变形的进行,等轴α相晶粒发生细化;在950～980℃范围内变形时,随着变形温度的升高,初生α相晶粒尺寸逐渐增大,在980℃条件下变形时,预锻件整体范围内晶粒尺寸波动较大;随着变形速率的增加,初生α相晶粒尺寸减小;在0.5和1.0mm/s条件下成形时,温度对晶粒尺寸影响比较小,而在0.1mm/s条件下变形时,随着温度的升高,晶粒长大比较严重;随摩擦因子的增大,平均晶粒尺寸有所减小,整个锻件晶粒尺寸分布的不均匀性增加。     

硅对Mg2Si/ZM5复合材料组织和性能的影响

在真空感应炉中氩气保护下制备材料，采用OM，SEM，EDAX和XRD及拉伸试验，研究分析了硅对原位反应自生Mg2Si/ZM5复合材料铸态显微组织和性能的影响规律。结果表明，反应添加物Si在ZM5合金中形成了高熔点、高硬度的Mg2Si强化相，明显地提高了材料的室温与高温强度，如Si的质量分数为1.5％时，室温抗拉强度与屈服强度提高幅度分别可达20.1％和61.5％，Si的质量分数为1.0％时，高温抗拉强度与屈服强度提高幅度分别可达14.9％和25.7％；Mg2Si相的形貌随着硅含量的不同而变化，如Si的质量分数为0.5％时，主要生成细小短棒状或片状共晶Mg2Si相，Si的质量分数大于1％时，则出现了粗大块状或汉字状初生Mg2Si相和片状或短棒状的共晶Mg2Si相；由于所生成的Mg2Si相本身是一种脆性相，使得该材料呈现出解理断裂，降低了材料的塑性。     

Volume change during the solidification of grey cast iron: its relation with the microstructural variation,comparison between experimental and theoretical analysis

The expansion/contraction during the solidification of grey cast iron was studied using Linear Variable Differential Transformer (LVDT). The experiments were conducted with and without melt treatment. Two types of inoculant used for melt treatment: ASSC (Si, Ca, Sr & Al) and MBZCAS (Si, Ca, Zr, Ba, Mn & Al). Microstructural investigations carried out to quantify the eutectic cells, undercooled graphite, primary austenite and secondary dendritic arm spacing (SDAS). It was found that the casting shows hardly any shrinkage during early solidification but in the eutectic region, the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS promotes more flake graphite, and ASSC does not increase eutectic cells much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth, decreases undercooled graphite and SDAS. As a result, the volume expansion changes in the eutectic region.     

DISTRIBUTION OF SULFUR IN HIGH TEMPERATURE PHASES OF CAST IRON

The distribution of subversive element sulfur in high temperature phases during solidificationof cast iron was investigated by means of liquid quenching method and autoradiography.Theresults show that in grey cast iron,sulfur is concentrated in the liquid,flake graphite and in theperipherial area of D-type supercooled graphite eutectic cells,but less sulfur is in austenite.Besides,the content of sulfur in A-type graphite is higher than that in D-type graphite,andsulfur content in eutectic austenite is a little higher than that in primary austenite.While,innodular graphite cast iron less sulfur is in liquid and austenite,but more in nodular graphite.The blackness of the spots on the emulsion film corresponds to the atomic percentage ofradioactive substances located on the surface of the specimen.     

MODIFICATION EFFECT OF Sr ON Al-Si ALLOYS

By inserting the single crystal silicon seeds into Sr modified Al-22wt-% Si alloy melts,thefact that nucleation and growth of Si-phase are affected by Sr addition has been confirmed.Itis suggested that this effect is caused by the adsorption of Sr on{111}_(si),and the modificationof eutectic structure results from the variation of leading phase in the eutectic from Si to α-Al.     

Zn—2.75%Cu合金定向凝固组织及对流的影响

研究了Zn-2.75%Cu合金在传统Bridgeman法和ACRT－B法下定向凝固组织的差别。着重讨论了生长速度和液相强制对流对Zn-Cu包晶定向凝固组织的影响。实验发现,在Bridgeman法定向凝固过程中,生长速度的增加使得液相中的温度梯度减小,一次枝晶间距减小,一次枝晶间距与生长速度和温度梯度的关系式为：λ1=0.6064R^-0.25GL^-0.5。强制对流使得一次枝晶发生分叉和偏转。并且随着对流强度的加大,一次枝晶间距降低,二次枝晶的生长被抑制。包晶反应的存在,使得枝晶的尖端和二次枝晶熔解,造成了固相中枝晶和初生枝晶的差别。     

Formation of eutectic intermetallic rosettes by entrapment of liquid droplets during cellular columnar growth

We study the formation of -Al-(Fe,Mn)-Si phase intermetallic particles in a directionally-solidified model Al–0.5Fe–1.0Mn–0.2Si (wt%) alloy. In this the aluminium matrix has a cellular-columnar grain structure. Secondary phases are expected to form from solute-partitioned liquid at the cell boundaries. However, spherical rosettes of eutectic -phase can be found within the cells. Evidence is presented that these are formed from liquid droplets trapped when a cell splits and then coalesces. The intercellular regions of the as-cast alloy are primarily occupied by metastable Al₆(Fe,Mn) eutectic particles. However, these may transform to the stable -phase, either by a ternary peritectic transformation during solidification, or by the eutectoid 6-to- transformation during the period in which the ingot cools to room temperature.