---

In this study a feed forward back propagation artificial neural network (ANN) model was established to predict Vickers microhardness in aluminum-alumina nanocomposites which have been synthesized by mechanical alloying and hot pressing. Volume percent of reinforcement, size of nanoparticles, force in microhardness test; and mechanical alloying parameters, such as time, ball to powder ratio (BPR) and speed of ball mill were used as the inputs and Vickers microhardness as the output of the model. Effective parameters in training such as learning rate, hidden layers and number of neurons, were determined by trail and error due to amount and percentage of errors. Regression analysis in train, validation and test stages; and mean squared error were used to verify the performance of neural network. Average error of predicted results was 2.67% or 2.25 Vickers. Also mean squared error for validation data was 7.76. As can be expected, ANN methods reduce the expenses of experimental investigations, by predicting the optimum parameters.

---

---

Thermal spraying is economical and rapid coating process that creates a rough and clean surface. As a result it can be used for applying the interlayer in transient liquid phase bonding. In the present study, transient liquid phase bonding Al 2024 to Ti-6Al-4V was investigated using brass interlayer, where the interlayer was Cu-Zn foil Cu-Zn thermal spray coat on Al substrate, respectively. The results show that by using thermal spray coat as interlayer, because of the formation of different defects that can be considered as diffusion channels, diffusion potential of Ti and Al becomes higher at the interface. It is concluded that the mechanism of bonding formation involves the diffusion of Cu into Al and Ti base materials and formation of TiAl، TiAl، Cu₂ Al and AlCuMg phases and also diffusion of Cu through Al grain boundaries and formation of eutectic phases across the grain boundaries. The formation of these intermetallic phases was confirmed by energy dispersive spectroscopy and X-ray diffraction. Dissolution of the base metals in the joint area and the isothermal solidification process of the thermal sprayed interlayer is more and faster than the foil interlayer. The joint with thermal spray brass coat as interlayer, gives higher shear strength of 25 MPa in comparison with the case of using brass foil as interlayer (14.6 MPa). The decrease in bond strength can be attributed to aggregation and growth of the brittle intermetallics near the joint interface due to lower diffusion potential of Ti and Al in the joint zone.

---

In this study, the effect of multidirectional forging (MDF) was studied on the microstructure and mechanical properties of Ti-modified Si_P/ZA22 composite containing 4 and 8 wt. % Si. The forging process was performed at 100 °C by two and five passes. Based on the obtained results, Ti modification refined the coarse primary dendrites, and reduced the size of primary Si (Si_P) particle as well as grains. Applying MDF also gradually eliminated the dendritic structure, promoted fine distribution of Si_P particles, second phases, and porosities in the microstructure. According to the image analysis results, the average size of Si_P particles in as-cast composite reduced from 25 and 30 μm to about 6 and 7 μm, respectively in 5-pass MDFed composites containing 4 and 8 wt. % Si. The mechanical properties results also showed work softening during the MDF where after two-pass MDF the hardness and tensile strength of the base sample reduced by 30 and 25%, while its elongation and toughness improved by 120 and 325%, respectively. In MDFed composites, the presence of Si_P particles maintains the hardness and strength. According to the results, in the case of 2-pass MDFed composite containing 4 wt. % Si the hardness and tensile strength reduced by 18 and 2%, respectively, but the elongation and toughness increased by 25 and 175%, respectively.  

---

The defectless microstructure of metal matrix composites, the uniform distribution of particles and their good properties are determined by the production parameters and the base material and reinforcement. In this study, high-energy planetary ball mill was used to fabricate Al6063-SiC composite powder. Aluminum chips were milled with different time and ball to powder weight ratio (BPR) in high energy planetary ball mill. The resulting powder was mechanically alloyed by adding different weight percentages of silicon carbide (SiC) and BPRs at different times. During the milling process under argon atmosphere, stearic acid was used as a process control agent (PCA) to prevent excessive cold welding and agglomeration of the powder. After mechanical alloying, the effect of alloying time, BPRs and weight percentage of silicon carbide, on the obtained composite powder were examined morphologically by particle size analysis (PSA), field emission scanning electron microscope (FESEM), and the fuzzy compounds by X-ray diffraction (XRD) spectroscopy. According to the X-ray diffraction pattern of the samples, grain size was calculated using the Williamson-Hall model. The results of mechanical milling and alloying process have shown that in short milling times with high BPRs composite powder with finer particle size could be achieved. Also, the presence of silicon carbide reinforcing particles accelerates the process of mechanical alloying and further reduces the particle size.