Modification of Eutectic Si and Refinement of Eutectic Grain in Al-Si-Mg Alloys by CrB2 and Sr Addition

In order to obtain high-strength and high-ductility Al–Si–Cu–Mg alloys, the present research is focused on optimizing the composition of soluble phases, the structure and morphology of insoluble phases, and artificial ageing processes. The results show that the best matches, 0.4 wt% Mg and 1.2 wt% Cu in the Al–9Si alloy, avoided the toxic effect of the blocky Al2Cu on the mechanical properties of the alloy. The addition of 0.6 wt% Zn modified the morphology of eutectic Si from coarse particles to fine fibrous particles and the texture of Fe-rich phases from acicular β-Fe to blocky π-Fe in the Al–9Si–1.2Cu–0.4Mg-based alloy. With the optimization of the heat treatment parameters, the spherical eutectic Si and the fully fused β-Fe dramatically improved the ultimate tensile strength and elongation to fracture. Compared with the Al–9Si–1.2Cu–0.4Mg-based alloy, the 0.6 wt% Zn modified alloy not only increased the ultimate tensile strength and elongation to fracture of peak ageing but also reduced the time of peak ageing. The following improved combination of higher tensile strength and higher elongation was achieved for 0.6 wt% Zn modified alloy by double-stage ageing: 100 °C × 3 h + 180 °C × 7 h, with mechanical properties of ultimate tensile strength (UTS) of ~371 MPa, yield strength (YS) of ~291 MPa, and elongation to fracture (E%) of ~5.6%.

Download Full-text

Role of Bi and Ca Additions in Controlling the Microstructure of Sr-Modified 319 Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.519-521.1257 ◽

2006 ◽

Vol 519-521 ◽

pp. 1257-1264 ◽

Cited By ~ 2

Author(s):

S. El Hadad ◽

A.M. Samuel ◽

F.H. Samuel ◽

H.W. Doty ◽

S. Valtierra

Keyword(s):

Electron Microscopy ◽

Particle Size ◽

Image Analysis ◽

Mg Alloys ◽

Microstructural Characteristics ◽

Optical And Electron Microscopy ◽

Modification Effect ◽

Eutectic Si ◽

Mg Addition

The role of bismuth (50 to 9000 ppm) and calcium (50 to 200 ppm) additions on the microstructural characteristics in Sr-modified 319 alloys (with/without 0.4 wt% Mg addition) were investigated using optical and electron microscopy, and image analysis. It was found that the modification effect of Sr continuously diminished with Bi addition up to ~3000 ppm Bi; further Bi addition led to the modification of the Si particles due to the presence of Bi. In the Ca-containing alloys, a coarse eutectic Si structure resulted with Ca additions of 50 ppm, due to the formation of Alx(Ca,Sr)Siy compounds. Increased Ca additions (up to 200 ppm) did not alter the Si particle size. The Alx(Ca,Sr)Siy phase particles appeared in rod-like form in the Sr-modified alloys and in plate-like form in the 319+0.4 wt% Mg alloys. MgO, Al2O3, and AlP particles appear to act as nucleants for the precipitation of the plate-like Alx(Ca,Sr)Siy phase.

Download Full-text

Influence of the Solution and Artificial Aging Treatments on the Microstructure and Mechanical Properties of Die-Cast Al–Si–Mg Alloys

Metals ◽

10.3390/met12010071 ◽

2021 ◽

Vol 12 (1) ◽

pp. 71

Author(s):

Ho-Jung Kang ◽

Jin-Young Park ◽

Yoon-Suk Choi ◽

Dae-Hyun Cho

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Solid Solution ◽

Artificial Aging ◽

Solution Treatment ◽

Mg Alloys ◽

Needle Type ◽

Heat Treated ◽

Die Cast ◽

Eutectic Si

Heat treatment is widely used to improve the properties of Al–Si–Mg alloys and its outcomes are influenced by the parameters applied during the treatment. This study describes the effect of the solution and artificial aging treatments on the microstructure and mechanical properties of die-cast Al–Si–Mg alloys. The microstructure of the as-cast Al–Si–Mg alloy was mainly composed of α-Al, complex needle-type eutectic Si particles, Mg2Si, and α-AlFeMn. The complex needle-type eutectic Si particles disintegrated into spheroidal morphologies, while the Mg2Si was dissolved due to the solid solution treatment. The maximum yield strength (YS) and ultimate tensile strength (UTS) values were 126.06 and 245.90 MPa at 520 °C after 90 min of solution heat treatment, respectively. Although the YS and UTS values of the Al–Si–Mg alloys reduced due to the solution treatment, the elongation (EL) of the solid solution heat-treated Al–Si–Mg alloys was improved in comparison to that of the as-cast Al–Si–Mg alloy. The maximum YS and UTS of 239.50 and 290.93 MPa were obtained after performing artificial aging at 180 °C for 180 min, respectively. However, the EL of the aging heat-treated alloy was reduced by a minimal value.

Download Full-text

Rare Earth Metal-Based Intermetallics Formation in Al–Cu–Mg and Al–Si–Cu–Mg Alloys: A Metallographic Study

Advances in Materials Science and Engineering ◽

10.1155/2018/7607465 ◽

2018 ◽

Vol 2018 ◽

pp. 1-15 ◽

Cited By ~ 3

Author(s):

A. M. Samuel ◽

E. M. Elgallad ◽

M. G. Mahmoud ◽

H. W. Doty ◽

S. Valtierra ◽

...

Keyword(s):

Eutectic Reaction ◽

Earth Metal ◽

Nucleation Site ◽

Mg Alloys ◽

Significant Drop ◽

Metallographic Examination ◽

Gray Phase ◽

White Phase ◽

Eutectic Si ◽

Fixed Composition

This study was conducted on Al–Cu–Mg and Al–Si–Cu–Mg alloys containing either 5%La or 5%Ce. Two levels of Ti addition were examined, i.e., 0.05% and 0.15%. Thermal analysis was the only technique used to obtain castings, from which samples were then sectioned for metallographic examination. Based on the results obtained, the following points may be highlighted. Addition of a fairly large amount of RE metals (La or Ce) leads to the appearance of several peaks in the solidification curve between the precipitation of the primary α-Al phase and the (Al–Al2Cu) eutectic reaction. Although a significant drop in the eutectic temperature is caused by the addition of 5%La or Ce, the corresponding modification of the eutectic Si is marginal. Two main types of intermetallics were documented: a gray phase in the form of sludge with a fixed composition and a white phase in the shape of thin platelets. Due to the high affinity of RE to react with Si, Fe, and Cu, several compositions were obtained explaining the observed multiple peaks in the solidification curve. Judging by the morphology of the gray phase, it is assumed that this phase is precipitated in the liquid state and acts as a nucleation site for the white phase. Lanthanum and Ce can substitute each other.

Download Full-text

Accelerating pore nucleation and eutectic Si growth kinetics by increasing Cu and Sc for Al-Si-Mg alloys: In-situ observation

Journal of Alloys and Compounds ◽

10.1016/j.jallcom.2021.159173 ◽

2021 ◽

Vol 869 ◽

pp. 159173

Author(s):

Mingshan Zhang ◽

Keli Liu ◽

Bing Wang ◽

Tingting Liang ◽

Jiaqiang Han ◽

...

Keyword(s):

Growth Kinetics ◽

Mg Alloys ◽

In Situ Observation ◽

Eutectic Si ◽

Pore Nucleation

Download Full-text

Spheroidization and Coarsening of Eutectic Si Particles in Al-Si-Based Alloys

Advances in Materials Science and Engineering ◽

10.1155/2021/6678280 ◽

2021 ◽

Vol 2021 ◽

pp. 1-16

Author(s):

Mohamed Ibrahim ◽

Mohamed Abdelaziz ◽

Agnes Samuel ◽

Herbert Doty ◽

Fawzy Samuel

Keyword(s):

Mg Alloys ◽

Spherical Particles ◽

Heat Treated ◽

Eutectic Si ◽

Cast Alloys ◽

Si Content ◽

Solutionizing Time

The present study was carried out on three Al-Si cast alloys viz., 319, 356, and 413 alloys, solidified at 8°C/s. Samples from 319 and 413 alloys were solution heat-treated at 510°C, whereas samples from 356 alloy were solutionized at 550°C, for up to 1200 h. The results reveal that complete spheroidization of eutectic Si particles in terms of achieving individual spherical particles cannot be achieved in most Al-Si-Cu-Mg alloys even after a solutionizing time of 1200 h which contradicts with the existing theory. Addition of Sr to Cu-free 356 alloy could lead to complete spheroidization after 1200 h at 550°C if the alloy was solidified at 8°C/s. Besides the dissolution theory of Ostwald, coarsening of Si particles can as well take place by impingement, fusion, and agglomeration. Increasing the Si content makes it difficult to achieve spheroidization, i.e., fragmentation and coarsening. Results obtained from observations of deeply etched samples (3D) contradict those obtained from polished samples (2D).

Download Full-text

Modification of Eutectic Si and Refinement of Eutectic Grain in Al-Si-Mg alloys by CrB2and Sr Addition

Light Metals 2016 ◽

10.1002/9781119274780.ch119 ◽

2016 ◽

pp. 711-714

Author(s):

J.H. Li ◽

P. Schumacher

Keyword(s):

Mg Alloys ◽

Eutectic Si

Download Full-text

Electron-Probe Quantitative Energy-Dispersive Analysis of Trace Magnesium Concentrations in Ag-Mg Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010016501x ◽

1996 ◽

Vol 54 ◽

pp. 510-511

Author(s):

R. B. Marinenko

Keyword(s):

Electron Probe ◽

Energy Dispersive Spectrometry ◽

Mg Alloys ◽

Energy Dispersive ◽

Energy Dispersive Analysis ◽

High Tc ◽

Alloy Wire ◽

High Tc Superconductor ◽

Eds Analysis ◽

Superior Mechanical Properties

Internally oxidized Ag-Mg alloys are used as sheaths for high Tc superconductor wires because of their superior mechanical properties. The preparation and characteristics of these materials have been reported. Performance of the sheaths depends on the concentration of the magnesium which generally is less than 0.5 wt. percent. The purpose of this work was to determine whether electron probe microanalysis using energy dispersive spectrometry (EDS) could be used to quantitate three different Ag-Mg alloys. Quantitative EDS analysis can be difficult because the AgL escape peak occurs at the same energy (1.25 keV) as the Mg Kα peak. An EDS spectrum of a Ag-Mg alloy wire is compared to a pure Ag spectrum in Fig. 1.

Download Full-text