A356合金细化处理效果的孕育和衰退

通过考察A356合金在静置过程中细化效果的变化，研究了亚共晶铝硅合金细化处理的孕育期和衰退期。细化处理的孕育期的形成是由于细化初期的溶质过冷度小造成的，随着溶质Ti含量的增加，溶质过冷度增大，从而激活更多的形核质点，限制枝晶生长；长时间静置后，尽管细化元素Ti含量基本不变，但是成分偏析倾向加剧，形核质点粗化并沉淀，有效核心减少，出现细化效果衰退；采用预细化合金锭可以缩短甚至消除细化处理的孕育期。     

稀土对过共晶Al-Si合金P变质效果的影响

研究了加入稀土元素La对P变质Al-18Si合金中Si的形态及尺寸的影响，结果表明：稀土元素La的加入优化了P的变质效果，在细化初晶Si的同时变质了共晶Si，并且明显减缓了P变质初晶Si的粗化趋势，使变质效果至少可维持6h以上，通过扫描电镜测定了稀土元素La在合金中的分布，并分析讨论了稀土元素La对P变质效果影响的机理和作用。     

大型异形铝铸件的铸造工艺研究

大型异形铝铸件,铸造工艺难度较大,常需依赖于丰富的生产经验辅之以计算机凝固模拟分析技术。针对不同的形状,制定相应的铸造工艺。对管体、轮毂、支腿垫块、螺旋桨等典型产品较为成熟的生产工艺进行介绍。通过对这些典型铸件的工艺案例进行分析,探讨大型异型铝铸件的铸造工艺设计方法。     

XPS investigations of electrochemically formed passive layers on Fe/Cr-alloys in 0.5 M H2SO4

Passive layers on Fe20Cr and Fe15Cr were prepared by anodic oxidation in 0.5 M H₂SO₄ and were investigated by X-ray photoelectron spectroscopy. The preparation of the sputter-cleaned samples and their transfer to the ultrahigh vacuum was performed under protection of purified argon without any contact to the laboratory atmosphere. The prepassive layer consists of a homogeneous film with Cr(III)hydroxide and Cr(III)-sulphate with a low content of Fe(II). In the passive potential range a bilayer structure with enrichment of Cr(III)-oxides with an outer hydroxide and an inner oxide part is formed. Iron exists only in a bivalent oxidation state. In the transpassive potential range a pronounced change of the layer composition was observed: The outer part of the transpassive layer is formed predominantly by Fe(III) species whereas the inner part still contains a strong enrichment of Cr₂O₃.     

大型铝合金叶片金属型铸造工艺分析

针对铝合金叶片的铸造缺陷，分析指出浇注位置、浇注系统设计、型腔排气和充型温度场是造成铸造缺陷的主要因素，据此，有针对性地提出了铸型倾斜、平浇竖冷、沿分型面开设排气槽、改变涂料层厚度以及调整凝固顺序等改进措施，其效果在生产中得到验证。     

Steric hindrance as a rate controlling step in stress corrosion cracking

The effect of steric hindrance in the stress corrosion cracking (SCC) of Ag-15Pd (a/o) in AgI forming solutions was studied at room temperature. The solutions used were 1 M KI at a potential higher than that of AgI formation, and iodine dissolved in different n-alcohols. It was found that Ag-15Pd (a/o) is susceptible to intergranular stress corrosion cracking in those solutions. The SCC susceptibility measured as percentage of elongation to rupture and crack propagation rate is related to the size of the active species. While in KI aqueous solutions, as well as in iodine saturated benzene or iodine saturated toluene, the rate controlling step (RCS) was the reaction at the tip of the crack, in alcoholic-iodine solutions, the diffusion rate of the iodine containing molecules became the RCS.     

冷却方式对Zn-Cu包晶合金微观组织的影响

对采用不同冷却速度、不同散热条件的铸型得到的Zn-2.98Cu包晶合金的微观组织进行了研究.研究表明:在常规的砂型和金属型铸锭中,其微观组织为ε相 η相基体;在具有定向温度梯度的铸锭中,得到了定向的ε相枝晶 η相基体和定向的层片状(ε η)组织;并对层片状组织做了进一步分析,得到的Zn-Cu包晶合金层片间距平均值λ=4.06μm.     

Effect ofθ-alumina formation on the growth kinetics of alumina-forming superalloys

Alumina-forming ODS superalloys are excellent oxidation-resistant materials. Their resistance relies upon the establishment of a stable, slow-growing, and adherent -alumina. In the present investigation, these alloys exhibited unstable and relatively less adherent -alumina phase, which increased the oxidation rate in the transient stage and converted into -alumina in the later part of the exposure. The oxide-growth process was found to depend upon various parameters such as temperature, time, and presence of an active elecment in the superalloy. Characterization carried out by XRD, SEM/EDAX, and AES on oxidized ODS and non-ODS alloys demonstrated a significant influence of the active element, Y, on the transformation of - to -alumina. SIMS analysis of two-stage oxidation at 900°C for two different durations evidently showed that the change in the transport process is due to -to--alumina transformation. On the basis of these results, a new and consistent mechanism is proposed to explain the influence of -alumina and its transformation on growth kinetics and the effect of yttrium on the transformation leading to good scale adherence and oxidation resistance.     

耐热铸造镁合金的研究现状及其发展趋势

耐热铸造镁合金在航空航天以及汽车工业等领域得到了广泛应用。本文主要介绍了Mg-Al系、Mg-Zn系和Mg—RE系耐热铸造镁合金的研究现状；对新型高性能耐热镁合金的发展趋势提出了一些见解，指出，合金化方法作为解决镁合金高温性能不足的最有效的手段之一，应该进一步通过优化合金元素组合，进行有效的合金设计，解决铸造镁合金在耐高温、抗蠕变等方面存在的问题。     

WE54镁合金中析出相的特点

WE54(Mg-5.4Y-2.3Nd-1.6Gd-0.5Zr)镁合金试样在铸态、T4和T6状态下,呈现出不同的显微组织形貌特征和微区化学成分,而且力学性能也随着处理工艺的不同而发生变化。采用金相显微镜、大功率X射线衍射仪、高分辨场发射扫描电镜及能谱仪分析研究了WE54合金的微观组织形貌、析出相以及微区化学成分的变化。结果表明,WE54合金在铸造状态下,Mg12Nd和Mg24Y5两种新相沿着晶界析出,呈现出网状结构,稀土Gd完全固溶在基体之中,在晶内和晶界析出物的微区化学成分分析中没有发现Gd;经过固溶处理后,铸态时沿晶界分布的大块析出物几乎全部固溶于基体Mg之中,力学性能有所提高;经过人工时效后,晶内析出大量细小的新相。经过对比试样沿横向和纵向析出相的特点,确定该析出相为片状结构。析出相沿3个方向排列分布,而且3个方向之间夹角互成120°,呈现出严格的位向关系,合金的强度进一步得到提高,但伸长率有所降低。