scholarly journals Phase transformations during the crystallization of the AK7 alloy, neutralization of the harmful effect of iron by treating the melt with a pulsed electric current

2020 ◽  
Vol 96 (4) ◽  
pp. 17-29
Author(s):  
A.G. Prigunova ◽  
Keyword(s):  
Mechanical Properties ◽  
Phase Transformations ◽  
Electric Current ◽  
Intermetallic Compounds ◽  
Volume Fraction ◽  
Cluster Structure ◽  
Harmful Effect ◽  
Study Phase ◽  
Current Frequency ◽  
Pulsed Electric Current

The method of quenching-microstructural analysis, the so-called "stop-quenching", was used to study phase transformations during crystallization of the AK7 casting alloy of the Al-Si-Mg system. The alloy is smelted from scrap and waste, therefore it contains a large amount of impurities, including iron, copper. It was found that the formation of the structure of the AK7 alloy is carried out in the course of the following reactions: 1. Р → Аlα. 2. P → α-(Fe, Mn) 3Si2Al15 + Alα. 3. P → β-FeSiAl5 + Alα. 4. P + β-FeSiAl5 → α-(Fe, Mn, Cu)3Si2Al15. 5. P → β-FeSiAl5 + Si + Alα. 6. P → β-FeSiAl5 + α-(Fe, Mn, Cu)3Si2Al15 + Si + Alα. At the last stages of crystallization, eutectics are formed, which include phases with magnesium and copper: Mg2Si, π-FeMg3Si6Al8, W-Cu2Mg8Si6Al and θ-CuAl2. The transformation P → β + Si + Alα is realized both by the mechanism of cooperative growth of the β, Si, and Alα phases, and by the formation of double eutectics: P → Si + Alα and P → β + Alα, which grow simultaneously in the same temperature range from various centers of crystallization. The four-phase eutectic transformation P → β + α + Si + Alα is carried out according to the type of double or triple eutectic reactions: P → Si + Alα; P → α + Alα; P → β + Alα; β + Si + Alα. The main iron-containing phase in the AK7 alloy is the needle-shaped intermetallic compound β-FeSiAl5 - a stress concentrator, which leads to a decrease in mechanical properties. In this work, the neutralization of the harmful effect of iron was carried out by treating the melt with a unipolar pulsed electric current, under the influence of which the cluster structure of the melt changes. During crystallization, instead of β, a branched phase α is formed. The ratio of intermetallic compounds β and α depends on the processing modes. With optimal parameters of density and current frequency, at which the volume fraction of the branched phase α is the largest, the strength of the AK7 alloy increases by 32.1%, the hardness by 16.7%, and the relative elongation by 2.5 times, bringing its mechanical properties closer to the primary alloy AK7h. Keywords: aluminum-silicon alloys, phase transformations, iron-containing intermetallic compounds, growth forms, treatment of the melt with an electric current.

MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF AMORPHOUS Al–Cu–Ti METAL FOAMS SYNTHESIZED BY SPARK PLASMA SINTERING

2017 ◽  
Vol 24 (Supp02) ◽  
pp. 1850022
Author(s):  
MAOYUAN LI ◽  
LIN LU ◽  
ZHEN DAI ◽  
YIQIANG HONG ◽  
WEIWEI CHEN ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Intermetallic Compounds ◽  
Spark Plasma Sintering ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Metal Foams ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Xrd Patterns

Amorphous Al–Cu–Ti metal foams were prepared by spark plasma sintering (SPS) process with the diameter of 10[Formula: see text]mm. The SPS process was conducted at the pressure of 200 and 300[Formula: see text]MPa with the temperature of 653–723[Formula: see text]K, respectively. NaCl was used as the space-holder, forming almost separated pores with the porosity of 65 vol%. The microstructure and mechanical behavior of the amorphous Al–Cu–Ti metal foams were systematically investigated. The results show that the crystallinity increased at elevated temperatures. The effect of pressure and holding time on the crystallization was almost negligible. The intermetallic compounds, i.e. Al–Ti, Al–Cu and Al–Cu–Ti were identified from X-ray diffraction (XRD) patterns. It was found that weak adhesion and brittle intermetallic compounds reduced the mechanical properties, while lower volume fraction and smaller size of NaCl powders improved the mechanical properties.

Binder-Free Tungsten Carbide Fabricated by Pulsed Electric Current Sintering

2007 ◽  
Vol 534-536 ◽  
pp. 1153-1156 ◽  
Author(s):  
Koji Shimojima ◽  
Hiroyuki Hosokawa ◽  
Takeshi Nakajima ◽  
Masahiko Mizukami ◽  
Yoshiharu Yamamoto
Keyword(s):  
Mechanical Properties ◽  
Tungsten Carbide ◽  
Electric Current ◽  
Applied Pressure ◽  
High Hardness ◽  
Maximum Temperature ◽  
Pulsed Electric Current ◽  
Binder Free ◽  
Field Assisted Sintering ◽  
Sintering Condition

In this paper, we show some experimental results of binder-free WC sintered by Pulsed Electric Current Sintering (PECS) also known as Field Assisted Sintering Technology (FAST). These binder-free WC have extremely high hardness and stiffness. However, these mechanical properties are dependent on the sintering condition, e.g., maximum temperature, applied pressure, etc. We show some relationship between mechanical properties and sintering condition to improve to sinter the binder-free WC.

Mechanical Properties of Alumina Based Nanocomposites

2012 ◽  
Vol 527 ◽  
pp. 101-106 ◽  
Author(s):  
Erkka Kannisto ◽  
M. Erkin Cura ◽  
Erkki Levänen ◽  
Simo Pekka Hannula
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Electric Current ◽  
Critical Size ◽  
Rule Of Mixtures ◽  
Microstructure And Mechanical Properties ◽  
Nickel Particles ◽  
Pulsed Electric Current

To study the microstructure and mechanical properties of alumina nanocomposites, Al2O3/2.5 vol.% Ni and Al2O3/10 vol.% ZrO2 nanocomposites were consolidated by pulsed electric current sintering (PECS). Fracture toughness was found to increase by 13 % and 16 % respectively compared to reference alumina. Hardness increased slightly in Al2O3/Ni because of a fraction of nickel particles under the critical size (2 following the rule of mixtures. By investigating the results, causes of improved mechanical properties were critically evaluated.

scholarly journals The mutual effect of iron and manganese on microstructure and mechanical properties of aluminium –silicon alloy

10.30544/383 ◽  
2010 ◽  
Vol 16 (1) ◽  
pp. 11-24 ◽  
Author(s):  
Alireza Darvishi ◽  
Ali Maleki ◽  
Mehdi Mazar Atabaki ◽  
Mohammad Zargami
Keyword(s):  
Mechanical Properties ◽  
Intermetallic Compounds ◽  
Volume Fraction ◽  
Manganese Content ◽  
Mutual Effect ◽  
Manganese Concentration ◽  
Microstructural Investigation ◽  
High Concentrations ◽  
Different Content ◽  
Iron And Manganese

The effect of iron and manganese concentration on the morphology of complex intermetallics and their influence on the mechanical properties and microstructure has been studied in an Al-16.67 wt. % Si alloy with three content of iron (0.4, 1.2, 1.8 wt.%), and two different content of manganese, i.e. 0.6 and 0.9 wt.%. The intermetallic compounds are formed at high iron contents or at high concentrations of manganese with low iron. The microstructural investigation by Clemex software showed that the biggest intermetallic size reached the surface area of 12750 μm2, when the amount of iron was increased from 1.2% to 1.8% wt.%. It was also showed that the volume fraction of intermetallic compounds increases as the iron and manganese content increases. Formation of complex intermetallic phases with iron adversely affects tensile strength decreasing from 229MPa with 0.4 wt.% of iron to 187MPa when iron content was increased to 1.8 wt.%.

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