Mostafa Alizadeh

A Study on Hot Tearing Behavior of Al-1 Wt Pct Cu Alloy Under Various Strain Rates During Casting Process

Objective of this work is to study the generation of hot tears during solidification of Al-1 wt pct Cu alloy, which contain both columnar and equiaxed structures at various strain rates. To reach this goal, an experimental test was designed for applying tensile load on the solidifying shell. The shells were loaded at various pull-rates of 0.1, 0.2, and 0.3 mm/s. The produced samples were studied using scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy probe and metallography techniques. SEM images revealed that both segregated hot tear (i.e., filled or healed crack) and open hot tears were formed. Hot tears had created severely segregated zones with high concentration of Cu and Fe elements formed in between dendrite arms along the primary grain boundaries. In all cases, open hot tears were formed due to cracking of the segregated zones. With increasing strain rate, lengths of segregated hot tears were increased, moving closer toward the center of the cast. At the highest strain rate, segregated hot tears were formed in the equiaxed grain region along the primary grain boundary.

A study on effects of a new two-step strain induced melt activation process on characteristics of Al 7075 alloy

Abstract It is well-known that the strain induced melt activation process results in a globular microstructure which improves the hardness and the ultimate tensile stress. However, its disadvantage is degrading some other properties such as elongation and formability due to the presence of continuous and brittle intermetallic compounds along with the formation of eutectic structures at grain boundaries. Hence, the aim of this research is to introduce a new process called two-step strain induced melt activation to overcome these drawbacks and to improve the microstructure and the formability of Al 7075 alloy. This new process yielded a globular structure and modified the microstructure. Also, the resultant precipitates were discontinuous with a more homogeneous distribution and the eutectic mixture was eliminated. Moreover, the alloy formability and the hardness were effectively enhanced by performing a rolling process.

Corrosion Failure of the External Surface of Chlorinator’s Copper Pipes in a Water Disinfection Station

This work investigates the corrosion failure of the chlorinator’s copper pipes in a rural water disinfection station. For this purpose, some corroded samples were provided from the failed pipes and investigated using the X-ray diffraction (XRD) and the scanning electron microscope (SEM) equipped with the energy-dispersive X-ray spectroscopy (EDS). Also, an experimental setup was designed to study the role of the electrolyte formation on the copper pipes. This experimental setup demonstrated that the main factor of pipe failure was the formation of a corrosive electrolyte layer with varying chlorine (presented due to gas leakage) concentration during a day. The electrochemical impedance spectroscopy (EIS) confirmed that variations in the chlorine concentration had an unexpected effect on the corrosion rate. Furthermore, it was found that the main phase in the corrosion products was cupric chloride hydroxide (Cu2(OH)3Cl) with many porosities and cracks. These defects provide suitable places for the formation of the corrosive electrolyte and the following corrosion which ultimately led to the failure of the copper pipes.

Modification of microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al2O3 composite through semi-solid thermomechanical processing using variable loads

Abstract The microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al2O3 composite were modified through a thermomechanical processing technique. The powders were cold pressed and solid state sintered for 90 min under argon atmosphere. Thermomechanical processing was then applied to the solid state sintered samples, which consisted of cold pressing followed by partial remelting for 30 min under argon atmosphere. Four different loads in the thermomechanical processing were used to investigate the effects of compressive loads on the microstructures and the mechanical properties. The results revealed modifications in the microstructure of the thermomechanically processed samples with the optimum combination of properties in the sample modified by applying the load of 250 MPa. Increasing the thermomechanical processing load decreased the amounts of porosity by about 7 %, decreased the average grain size to about 4 μm, enhanced the compressive yield strength to about 295 MPa, and increased the microhardness values from 250 HV to 600 HV. In addition, the energy absorption capacity increased by about three times.