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Improving the Surface Properties of Gray Cast Iron through In-Situ Alloying
M. Khoobroo, A. Maleki, B. Niroumand,
Volume 36, Issue 3 (11-2017)
Abstract

Conventionally, alloying elements are being added to the whole melt; however, in this research in-situ surface alloying of gray cast iron was employed to improve surface properties of the castings. Wires of pure copper with diameters of 0.4 and 0.8 mm were inserted and fixed at bottom of sand molds before melting. Chemical composition analysis revealed the presence of copper from surface to a depth of 1 cm. Microstructural investigations indicated that graphite type changed from A to D and E. Moreover, the content of graphite phase decreased while that of pearlite increased at the surface. Hardness was higher at surface of copper added samples. Wear resistant of the in-situ surface alloyed samples was better than the no-copper added ones.
 


Determination of the Modified Hall-Petch Equation Constants and the Relationship Between the Microstructure and Mechanical Properties of AS7U3G Alloy
M. Lashani Zand, B. Niroumand, A. Maleki,
Volume 37, Issue 4 (3-2019)
Abstract
Mechanical properties of the alloys are a strong function of the average silicon particles size and the secondary dendrite arm spacing (SDAS). Modified Hall-Petch equation expresses the effects of these two microstructural parameters on the yield strength and ultimate tensile strength of the Al-Si based alloys. These microstructural parameters depen on parameters such as chemical composition, cooling rate and melt treatment. In this study, the effect of cooling rate on the  equation constants of the alloy were determined. For this purpose, the alloy was poured at 750 °C in three different molds including a sand mold, a preheated steel mold, and a water cooled steel mold. The Thermal and microstructural analysis showed that the cooling rate in the metal mold was 15.7 times higher than that of the sand mold, which resulted in a decrease of the SDAS from 54 micrometers to 17 micrometers. It was also found that by reducing the SDAS from 45 micrometers to 17 micrometers, the yield strength and tensile strength were increased by 16.5% and 6.5%, respectively. The modified Hall-Petch equation constants and the microstructure-mechanical properties relationships were then established by the microstructural and tensile test studies.

Morphological and Thermal Flux Analysis in as-Cast Al Alloy after Swarf Addition
H. Hadian, M. Haddad Sabzevar , M. Mazinani,
Volume 39, Issue 4 (2-2021)
Abstract
In this research, effect of swarf addition on the microstructure of die cast aluminum A380 alloy and the possibility of altering the alloy structure in the metallic die has been studied. The microstructure mainly consists of the α-phase, eutectic, intermetallic compounds and porosity. Since the alloy solidifies under non-equilibrium conditions, the Scheil equation with exact amount of equilibrium distribution, analyzed by SEM-Line scan around an intermetallic phase at different mixing times as well as governing equations of thermal analysis, was used to calculate the solid weight fraction. Finally, using the thermal flux analysis in the crucible, a scientific prediction on the optimal amount of swarf addition, mixing time and temperature, was made. The shape factor at an optimum temperature of 590 °C was measured as 0.643. According to the optical microscope images of the die cast samples, the addition method (adding it to the floor or to the surface) and increasing the injection temperature have a significant effect on the solid weight fraction, morphology of the α-phases and final microstructure of the alloy.
 

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