JOURNAL OF SCHOOL OF ENGINEERING
Year:2008 | Volume:20 | Issue:2|Papers Count:7

Cu-Al2O3 nanocomposite with different contents of Al2O3 has been successfully produced by using mechanochemical routs. This approach involves mechanical milling of Cu, Al, CuO in a low energy ball mill to produce Cu-Al2O3 composite. Different amount of initial Cu contents has been used to control the adiabatic temperature, Al2O3 particles size and Al2O3 content in the final products. The results of micro structure analysis with scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies showed that in the early stage of ball milling particles agglomeration occurred and subsequently a solid solution of Al in Cu, Cu(Al), formed. In next step reaction between soluted Al and CuO resulted in formation of fine Al2O3 particles and fracture of particles caused particles refinement. The results of Xray diffraction showed that Al2O3 particles were very fine and Cu crystallines were smaller than 30 nm after 72 hours ball milling.

In this paper the hot deformation behavior of Al-5083 commercial alloy is investigated. The aim is to investigate the formability of this alloy in hot tension under dynamic recrystallization. For this purpose, the material is thermo-mechanically processed. Then hot tensile tests are carried out at various temperatures and strain rates. Velocity jump tests are performed to determine stress-strain rate curves at various temperatures and strains. The microstructures are studied by optical and electron microscopy (SEM). It is found that the thermo–mechanical process resulted in a homogeneous distribution of fine precipitates. Dynamic recrystallization occurs during hot deformation of the AA5083. Maximum elongation about 250% is obtained at 450 oC and strain rate of 0.005 s-1. Maximum strain rate sensitivity (m) is 0.3. The failure surface is narrow and failure occurs by necking.

In the present research, laboratory thermomechanical processing using single pass hot compression was carried out on a low carbon Nb-Ti microalloyed steel to study the effect of deformation strain on the microstructural evolution. The objective is to understand how to attain a homogeneous, equiaxed and ultrafine ferrite (i.e. grain sizes < 3mm). Deformation schedules were conducted at two phase region (i.e. between Ar3-Ar1). Hot compression experiments were executed at constant temperature with strains from 0.25 to 1, and strain rate of 0.001 s-1. The physical processes that occur during deformation were studied by analyzing the true stress- true strain hot flow curves. Examination of the microstructural evolution was carried out by optical microscopy. Results show that at the deformation temperature lower than Ar3, in two phase region (a+g), there is not any evidence of dynamic softening events, and both austenite and ferrite are work hardened during the deformation. Very fine and equiaxed ferrite grains (EFG) of about 1.6 mm are obtained by deformation at 785oC for the strain of 1. This has been attributed to the occurrence of strain-induced transformation (SIT) of austenite to ferrite. With increasing strain, EFG size reduces and its volume fraction increases. It was inferred that the amount of strain plays an important role in SIT. This is by controlling the amount of activation energy required for SIT, when the specimen experiences the same strain rate.

In this investigation a new procedure has been developed for producing of Cast Iron parts. The Cast Iron parts were produced as two layers during of solidification. They had two zones, outer zone which was Grey Iron and inner zone which was Ductile Iron. At first, a complex cast part with a blind riser was designed. Second, some inoculants were placed into the blind riser on a wire screen for inoculation of melt. Finally, the micro structure from the outer skin toward the inner zone of the part was investigated by metallographic testing. Results showed that graphite’s in outer layers were from type of flack graphite, and the central zones were spherical graphite. In fact, at the first step of solidification, outer skin is solidified as Grey Iron. Then due to contact melt and inoculants material concurrent with cavity shrinkage as well as back pressure into the riser, a flow of inoculated melt move from the riser toward mold cavity. This phenomenon lead to formation of spherical graphite’s at the central zones. This procedure is very economic fore casting industries, because in this technique the blind riser has the role of a reaction cavity, instead of melt compensation.

Cu-Cr alloy was produced by chill-gravity casting in a wedge-shaped mould. Structure and composition were investigated using scanning electron microscope, XRD, and EDS analysis. The effect of cooling rate on the as-cast structure and properties and aging behavior was studied in details. Variations of lattice parameter, hardness and electrical conductivity were related to the chromium concentration in the solution. Maximum solubility of chromium was obtained at the tip of the wedge-shaped sample and measured about 1.7 atomic %. Effects of rolling on aging properties including hardness and electrical conductivity were also investigated.

A forming limit diagram (FLD) shows the various deformation states and represents the forming limits of sheet metal in the various sheet metal forming processes. In practice, experimental determination of a forming limit curve (FLC) is very time consuming procedure and requires special expensive equipments. Finite element simulation is an alternative method to predict FLD. In this paper, the effect of work hardening and anisotropy on FLC of drawing quality steel has been investigated and compared by using finite element method. For this purpose, the out-of-plane stretching test with hemispherical punch is simulated by finite element software ABAQUS 6.4. The limit strains, which are determined with localized necking, are specified by tracing the thickness strain and its first and second derivatives versus time at thinnest node. By doing this method for different specimens the strain based FLC has been determined. To validate the results, the numerical FLC has been compared with experimental and analytical forming limit curve. Then, the stress based FLD is determined by plotting the calculated principal stresses at the localized necking. Finally, the effect of work hardening and anisotropy has been investigated. The results shown that by increasing work hardening exponent the strain based FLC increases, but the stress based FLC does not change considerably. However, by increasing the value of normal anisotropy the stress based FLC increases, but the strain based FLC does not change considerably.

The main goal of this research was to evaluate the compressive deformation behaviour of multi-phase steel with retained austenite. Following a multi-stage heat treatment cycle on a low-alloy steel with 0.3 wt.%C, a multi-phase steel with considerable amount of retained austenite was produced.The determination of retained austenite in steel microstructures was performed by two different methods; image analysis of optical microscopic images and X-ray diffraction. The amount of retained austenite was measured to be around 18% in both techniques. Compressive deformation behaviour of the investigated steel was examined at different temperatures. A very high strength ratio (the ratio of flow stress at high strain value to yield strength) was obtained for the steel at room temperature exhibiting a characteristic combination of low yield strength and high work hardening rate. Achievement of high strength ratio was attributable to the presence of austenite phase in the steel microstructure and its transformation to hard martensite phase during straining (Transformation-Induced Plasticity Effect). The stress-strain response of the investigated steel at higher deformation temperatures was unusual. Flow stress and work hardening rate increased with an increase in temperature and reached their maximum values at the highest deformation temperature. Since retained austenite becomes more stable at higher deformation temperatures, formation of a transformation product other than martensite phase from austenite during straining was considered to be responsible for this unusual deformation behaviour. This transformation product was assumed to have high strength in order to give rise to a considerable microstructural strengthening effect.