Solidification microstructures and solid-state parallels: Recent developments, future directions

Get the phase diagram information you need at a price you can afford. Key Features: Peer reviewed by the Japanese Committee for Alloy Phase Diagrams. Updated through April 2000. Total number of diagrams = 2,332 (605 are new of greatly revised diagrams; among these 171 are not in Binary Alloy Phase Diagrams, 2nd Edition). Approximately 600 crystal structure tables of systems for which phase diagrams are unknown. You've been asking for a simple book containing just binary phase diagrams and crystal structure data. Desk Handbook: Phase Diagrams for Binary Alloys meets this need, and it presents the most current information. Updates the previous print compilation of binary phase diagrams by 10 years. Presents diagrams in consistent size. Shows the principal axis in atomic per cent, with a secondary axis in weight per cent. Includes an introductory article on phase diagrams and their use. Gives reference to the original literature source. This volume is the latest outgrowth of the phase diagram activity in which ASM International has been involved since 1978.

Desk handbook phase diagrams for binary alloys

The present paper systematically investigated the influence of solution and artificial aging heat treatments on the microstructures and mechanical properties of SLM-produced AlSi10Mg alloy parts. Due to the high cooling rate of SLM, an ultrafine eutectic microstructure in the as-built samples is characterized by spherical nano-sized network eutectic Si embedded in the Al matrix, which gives rise to significantly better tensile properties and Vickers micro-hardness. The solubility of Si atom in the Al matrix of as-built SLM samples is calculated to be 8.89 at%. With the increase in the solution temperature, the solubility decreases rapidly. The artificial aging causes the further decrease of the solubility of Si atoms in the Al matrix. Upon solution heat treatment, Si atoms are rejected from the supersaturated Al matrix to form small Si particles. With increasing the solution temperature, the size of the Si particles increases, whereas their number decreases. After artificial aging, the Si particles are further coarsened. The variation in size of Si particles has a significant influence on the mechanical properties of the AlSi10Mg samples. The tensile strength decreases from 434.25±10.7 MPa for the as-built samples to 168.11±2.4 MPa, while the fracture strain remarkably increases from 5.3±0.22% to 23.7±0.84% when the as-built sample is solution-treated at 550 °C for 2 h. This study indicates that the microstructure and mechanical properties of SLM-processed AlSi10Mg alloy can be tailored by suitable solution and artificial aging heat treatments.

Effect of heat treatment on AlSi10Mg alloy fabricated by selective laser melting: Microstructure evolution, mechanical properties and fracture mechanism

A selective laser melting and solution heat treatment refined Al-12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

The mechanical properties of Al–Si alloys are strongly related to the size, shape and distribution of eutectic silicon present in the microstructure In order to improve mechanical properties, these alloys are generally subjected to modification melt treatment, which transforms the acicular silicon morphology to fibrous one resulting in a noticeable improvement in elongation and strength. Improper melt treatment procedures, fading and poisoning of modifiers often result in the structure which is far from the desired one. Hence it is essential to assess the effectiveness of melt treatment before pouring. A much investigated reliable thermal analysis technique is generally used for this purpose. The deviation from the standard curve in thermal analysis helps in assessing the level of refinement of the Si structure. In the present review an attempt is made to discuss various aspects of modification, including mechanism, interaction of defects and non-destructive assessment by thermal analysis.

Modification of eutectic silicon in Al-Si alloys

Recent increasing applications for cast Al–Si alloys are particularly driven by the need for lightweighting components in the automotive sector. To improve mechanical properties, elements such as strontium, sodium and antimony can be added to modify the eutectic silicon from coarse and plate-like to fine and fibrous morphology. It is only recently being noticed that the morphological transformation resulting from eutectic modification is also accompanied by other, equally significant, but often unexpected changes. These changes can include a 10-fold increase in the eutectic grain size, redistribution of low-melting point phases and porosity as well as surface finish, consequently leading to variations in casting quality. This paper shows the state-of-the-art in understanding the mechanism of eutectic nucleation and growth in Al–Si alloys, inspecting samples, both quenched and uninterrupted, on the macro, micro and nano-scale. It shows that significant variations in eutectic nucleation and growth dynamics occur in Al–Si alloys as a function of the type and amount of modifier elements added. The key role of AlP particles in nucleating silicon is demonstrated.

Eutectic modification and microstructure development in Al–Si Alloys

From recent published data, it is still unclear whether combining additions of Na and Sr have synergistic effects or deleterious interactions. This paper clarifies the interactions between these two modifiers and investigates the effects of such interactions on alloy solidification and castability. It was found that combined additions of Sr and Na do not appear to cause improvement of the modification of the eutectic microstructure even after only a short period after addition. Na addition may promote Sr vaporization and/or oxidation kinetically, leading to a quicker loss of both modifiers, which is blamed for the rapid loss of the modification effect during melt holding. Quenching trials during the eutectic arrest indicate that addition of Sr into Na-modified melts does not alter the eutectic solidification behaviour. The effect of Na on eutectic solidification dominates, and the eutectic is observed to evolve with a significant dependency on the thermal gradient. Combining Sr and Na additions produced no beneficial effects on porosity and casting defects.

Combining Sr and Na additions in hypoeutectic Al–Si foundry alloys

Strontium is the most widely used and a very effective element for modifying the morphology of eutectic silicon, while Ti and B are commonly present in the commercial grain refiners used for Al-Si alloys. Systematic studies on the effects of combined additions of Sr and different AlTiB grain refiners on the Al + Si eutectic and primary aluminium solidification have been performed. While slight coarsening of both eutectic Si and primary aluminium grains occurs during holding, no obvious interactions are observed between Sr and AlTiB grain refiners when the addition level of grain refiners is low. As a result, a well-modified and grain refined structure was obtained. However, strong negative interactions between Sr and Al1.5Ti1.5B3 were observed as the addition level of the grain refiner increases. It was found that these interactions have a much more profound impact on the eutectic solidification than the primary Al solidification. The melt treated with combined additions of Sr and Al1.5Ti1.5B still shows good grain refinement efficiency even after losing its modification completely. The mechanism responsible for such negative interactions is further discussed. (c) 2006 Elsevier B.V. All rights reserved.

Effects of combined additions of sr and AlTiB grain refiners in hypoeutectic Al-Si foundry alloys

A method of forming a hypoeutectic aluminium silicon alloy including the steps of: forming an aluminium melt including greater than zero and less than about 12 wt % silicon, adding 20-3000 ppm of a eutectic modifying element selected from the group consisting of strontium, sodium, antimony, barium, calcium, yttrium, lithium, potassium, ytterbium, europium and mischmetal; and either adding nucleant particles and/or causing nucleant particles to be formed in the melt, the nucleant particles being selected from the group of TiSix, MnCx, AlP, AlBx and CrBx wherein x is an integer of 1 or 2.

Aluminium casting alloy

Eutectic modification with Sr, Na or Sb yields a refined fibrous silicon morphology which can improve the tensile ductility of cast Al-Si alloys. However, many companies choose not to use modifiers due to increased scrap rates and negligible beneficial effects on the mechanical properties because of alterations in the porosity characteristics of the castings. Here we report a novel method to modify Al-Si alloys which reduces the porosity of the castings while maintaining the well-modified silicon structure, thus producing consistent high performance Al-Si alloy castings. This new invention is based on the grain refinement of the Al-Si eutectic grains, or cells.

Liming Lu

Papers

Eutectic modification and microstructure development in Al–Si Alloys

Combining Sr and Na additions in hypoeutectic Al–Si foundry alloys

Effects of combined additions of sr and AlTiB grain refiners in hypoeutectic Al-Si foundry alloys

Aluminium casting alloy

Refinement of Al-Si Eutectic Grains - A Novel method to produce high integrity Al-Si Alloy Castings