Microstructure, Properties and Corrosion Resistance of As-Cast Al-12Si-1.0Mn-0.6Mg-xSc Alloys

Al-12Si-1.0Mn-0.6Mg-xSc (x = 0, 0.1, 0.2, and 0.3) alloys for electronic packaging were prepared by ingot metallurgy, and the microstructure, mechanical properties, thermo-physical properties and corrosion resistance were compared. A fine and dispersed Al3Sc phase is observed and the acicular β-Fe phase transforms into a Chinese character or massive α-Fe phase in the alloys with Sc addition. When the Sc content increases from 0 to 0.3%, the secondary dendritic arm spacing and the size of the eutectic Si reduce from 17.9 μm and 5.3 μm to 12.8 μm and 3.1 μm, respectively. Simultaneously, the morphology of eutectic Si changes from a rough long rod to an ellipsoid. The thermal expansion coefficient and thermal conductivity of the alloys reduce slightly with increasing the Sc content. The flexural strength of 291.9 MPa is obtained for the Al-12Si-1.0Mn-0.6Mg-0.3Sc, an increment of 20.4% as compared with the Sc-free alloy. Furthermore, the corrosion resistance of the alloys is improved by the minor Sc addition.

Effect of Alloying Elements on the Sr Modification of Al-Si Cast Alloys

Strontium-based modifier alloys are commonly adopted to modify the eutectic silicon in aluminum-silicon casting alloys by changing the silicon shape from an acicular to a spherical form. Usually, the modifier alloy necessary to properly change the silicon shape depends on the silicon content, but the alloying elements’ content may have an influence. The AlSr10 master alloy’s modifying effect was studied on four Al-Si alloys through the characterization of microstructural and mechanical properties (micro-hardness and impact tests). The experimental results obtained on gravity cast samples highlighted the interdependence in the modification of silicon between the Si content and the alloying elements. After modification, a higher microstructural homogeneity characterized by a reduction of up to 22.8% in the size of intermetallics was observed, with a generalized reduction in secondary dendritic arm spacing. The presence of iron-based polygonal-shaped intermetallics negatively affects Sr modification; coarser silicon particles tend to grow close to α-Fe. The presence of casting defects such as bifilm reduces Sr modification’s beneficial effects, and little increase in absorbed impact energy is observed in this work.

Thermal Analysis and Impart of Temperature Distribution on the Performance of Additive Manufactured Titanium Alloy Based Composite Coatings

Finite element numerical analysis can be used to solve problems of boundary values. The accuracy of model is depended on the meshing refinement. In aerospace industry, finite element analysis has been used by several researchers to know the influence of temperature distribution on the performance of additive manufactured component parts. Accuracy is better with finer mesh. Complex nature of the additive manufacturing process due to rapid heating and cooling made many researchers to adopt numerical investigation which is made easier than the experimental method. Proper modelling of the process must be thoroughly done for the numerical modelling results to be analyzed. The experiment of ternary titanium alloy of Ti-Al-Si-Cu was carried out with cladding machine of 3000 Watts (CW) Ytterbium Laser System (YLS-2000-TR). This machine is situated at the National Laser Centre in the Council of Scientific and Industrial Research (NLC-CSIR). The characterization was done using the standardization ASTM E3-11 procedure. The results shiw the impart of temperature distribution on the dendritic arm spacing in the microstructures. The rate of cooling imparts on the space between the dendritic arms. The more the space, the more the influence on the coating’s properties

The Microstructure and Properties of Low Carbon PM 625 Alloy for Marine-Based Application

The low carbon content powder metallurgy (PM) 625 alloy were manufactured by vacuum induction gas atomization (VIGA) and hot isostatically pressing (HIP) for marine-based application such as parts in the subsea Xmas tree. Corrosion experiment was performed in simulated deep seawater and subsea oil & gas service environment. The microstructures and properties of low carbon 625 alloy were comparably investigated with that of the as-cast alloy. The results indicated that the dendritic arm spacing (DAS) of the as-cast 625 alloy is 2 orders of magnitude higher than that of the powders, whereas the HIPed alloys possess a fine equiaxed grain structures without dendritic segregation and an average grain size of 14.5μm. No minor phase has been found beside the γ matrix in the original powders with different particle size. The tensile strength of low carbon PM 625 alloy is 26% higher than that of as-cast 625 alloy. PM 625 alloy possesses an excellent corrosion resistant in simulated deep seawater and oil & gas service environment for 30 days.

Influence of the Thermal Parameters on the Microstructure, Corrosion Resistance and Hardness on the Unidirectional Solidification of Al-10wt% Si-5wt% Cu Alloy

This study aims to correlate thermal parameters in the directional solidification of Al-10wt% Si-5wt% Cu alloy with the resulting microstructure and, in addition, with hardness and corrosion resistance. The results include primary dendritic arm spacing (PDAS), tip growth rate (VL), cooling rate (TR), scanning electron micrographs (SEM), hardness values and corrosion resistance parameters obtained by electrochemical impedance spectroscopy (EIS) and by the Tafel extrapolation method, conducted in 3% (m/v) NaCl solution at room temperature. The results show that coarser PDAS exhibit a tendency to increase in corrosion resistance, except in the positions with higher concentrations of the intermetallic compound Al2Cu, that surrounded by an aluminum rich phase tends to have a higher resistance to corrosion. The hardness values remained constant.

Effect of Ca on Microstructure and Mechanical Properties of Directionally Solidified Mg-Zn-Ca Alloys

The effect of Ca on the microstructure and mechanical properties of directionally solidified (DSed) Mg-3Zn-xCa alloys (x=0.2,0.5,0.8wt.%) was investigated in the present work. The results showed that the DSed samples with the growth rate of 120 μm/s had columnar dendritic structures and the primary dendritic arm spacing (PDAS) decreased with the content of Ca increase. The TEM result indicated that the growth orientation of the DSed Mg-Zn-xCa alloys was , which was independent of the content of Ca. The tensile tests at room temperature showed that the mechanical properties of the DSed Mg-Zn-xCa alloys were strongly affected by the content of Ca. The addition of Ca remarkably improved the ultimate tensile strength (UTS) and the yield strength (YS), while dramatically reduced the elongation (El). Prismatic slip and twinning were the main deformation mechanisms in tensile tests.

Characteristics and Formation Tendency of Freckle Segregation in Electroslag Remelted Bearing Steel

Undesirable macro segregation defects, freckles, restrict the commercial production of large-sized electroslag remelting (ESR) bearing steel ingots through degradation of the mechanical properties and service lifetime. In order to clarify the freckle characteristics and formation tendency as well as the formation mechanism, freckles from an industrial large-sized GCr15SiMn ESR ingot were investigated through structural and compositional analysis, along with simulation calculation. The results show that freckles consist of (Si, Mn, Cr)-enriched equiaxed grains and occur in about the 1/2 radius region at the middle-upper part of the ESR ingot, where the secondary dendritic arm spacing (SDAS) and solidification front angle are large but cooling rate is small. The absolute value of relative Rayleigh number, Ra, also reaches its maximum in the 1/2 radius region, with a liquid fraction of 0.3–0.5, corresponding to the region where freckles form. Based on the experimental and simulation results, to evaluate the freckle formation in industrial-scale GCr15SiMn ESR ingots, the threshold value of relative Ra, a freckle criterion considering the compositional and thermal effects, was determined to be about −0.023.

Numerical Model for Predicting Bead Geometry and Microstructure in Laser Beam Welding of Inconel 718 Sheets

A numerical model was developed for predicting the bead geometry and microstructure in laser beam welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy was employed for sweeping 1 mm wide circular areas for creating the weld seams, and a specific tooling was manufactured for supplying protective argon gas during the welding process. The numerical model takes into account both the laser beam absorption and the melt-pool fluid movement along the bead section, resulting in a weld geometry that depends on the process input parameters, such as feed rate and laser power. The microstructure of the beads was also estimated based on the cooling rate of the material. Features such as bead upper and bottom final shapes, weld penetration, and dendritic arm spacing, were numerically and experimentally analyzed and discussed. The results given by the numerical analysis agree with the tests, making the model a robust predictive tool.

Numerical Model for Predicting Bead Geometry and Microstructure in Laser Beam Welding of Inconel 718 Sheets

A numerical model was developed for predicting the bead geometry and microstructure in Laser Beam Welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy was employed for sweeping 1 mm wide circular areas for creating the weld seams and a specific tooling was manufactured for supplying protective Argon gas during the welding process. The numerical model takes into account both the laser beam absorption and the melt-pool fluid movement along the bead section, resulting in a weld geometry that depends on the process input parameters, such as feed rate and laser power. The microstructure of the beads was also estimated based on the cooling rate of the material. Features as bead upper and bottom final shapes, weld penetration and dendritic arm spacing were numerically and experimentally analyzed and discussed. The results given by the numerical analysis agree with the tests, making the model a robust predictive tool.