جستجوی مقالات مرتبط با کلیدواژه "ارتعاش مکانیکی" در نشریات گروه "مواد و متالورژی"

In the current study the effect of mold mechanical vibration during the solidification was studied on microstructure and corrosion behavior of Zn-4Si composite. According to the microstructural observation results, mechanical vibration substantially improved the SiP particle distribution and refined them. The image analysis results showed that mechanical vibration at 20, 40, and 60 Hz reduced the average size of SiP particles by 34, 55, and 75%, and increased their number density by 6, 16, and 36 times, respectively. Mechanical vibration at the 20, 40, and 60 Hz also decreased the average grain size by 50, 68, and 76%, respectively and increased the equiaxed zone in castings. The results of Tafel and impedance corrosion tests at 3.5 wt. % NaCl solution implied on increasing the corrosion current and shifting the corrosion potential to the more negative values in mechanically vibrated samples. The corrosion current of as-cast and 60 Hz samples were determined as -1.3610-5 and -2.3310-5 A, respectively. Mechanical vibration also reduces the corrosion resistance of samples where the resistance of 60 Hz sample (about 76 ohm) is lower than that of as-cast sample by about 45%. The increased density of grain boundaries and fine distribution of primary Si particles (as cathodic points) in the composite matrix are characterized as the most important factors decreasing the corrosion resistance of the composite. This is because they increased the number and interspacing of the galvanic cells within the matrix and exhibited appropriate locations for pitting.

In this study the effect of mechanical vibration (20 Hz, 40 Hz, and 60 Hz) during solidification on microstructure, hardness, and dry sliding wear resistance of Zn-4Si composite was studied. According to the results, Si addition led to the formation of primary Si (SiP) and eutectic Si (SiE) in the microstructure. This increased the hardness of Zn matrix from 30 BHN to more than about 60 BHN. However, uneven distribution (agglomeration) of SiP particles resulted in uneven hardness within the composite matrix. Applying the mechanical vibration during the solidification of composite improved the SiP particle distribution and refines them. According to the pin-on-disk sliding wear results, at the applied pressures of 0.25, 0.5, and 0.75 MPa, the sliding wear resistance of the modified composite (at the 60 Hz frequency) is higher than that of the as-cast composite by 50, 60, and 65%, respectively. Moreover, at the applied pressure of 0.75 MPa the average friction coefficient of mechanically-vibrated composite (60 Hz) is lower than that of as-cast composite by about 23%. Based on worn surface and wear debris analyses the substantial improvement of wear resistance in modified composites can be attributed to the improved tribolayer stability due to the strengthening effect of hard Si particles on the substrate material.

Semi-solid processes are amongst the novel methods of producing materials. The first method of these processes is introduced around 30 years ago. These methods include forming of a semi-solid, semi-molten mixture which can be produced by using casting or mechanical forming techniques. The key point for using these fabrication processes is to create a non-dendrite structure in a semi-solid mixture. Some tools and devices have introduced in semi-solid casting until now for example cooling slopes, mechanical vibration device and melt mixers. These devices are usually used for the purpose of reducing the grain size and also increasing the mechanical properties of alloys. Also, some studies approved that using of the controlled atmosphere reduces the amount of impurities and porosities into the product. Therefore, in this paper, the effect of different conditions on A380 aluminum alloy is investigated using a mechanical vibrator that capable of controlling the atmospheric environment. In following, Taguchi statistical method was used to analyze the data and also reduce the number of experiments. The statistical results showed that the temperature parameter had the highest effect, equal to 64%, in this alloy. Also, the second level of this parameter, which is 625°C, was selected as the most appropriate level. Also, vibration frequency, with an effect of 32%, ranks the second position and vibration time with an effect of 3% is in the third place, which both perform best at their highest chosen level.