Method for manufacturing A356 / SiC aluminum matrix composite with bismuth

Abstract

Metal matrix composites face problems in wettability and non-uniform distribution of reinforcing particles due to the ceramic nature of the reinforcing particles. This invention provides a method for producing an aluminum matrix composite by adding bismuth to the melt to improve wettability. The product of this invention is a composite in which the A356 alloy is reinforced with SiC particles. An electric furnace is used to produce the composite. After creating a semi-solid state, first pure bismuth and then SiC reinforcing particles are slowly added to the melt. After mechanically stirring the melt at a speed of 600 rpm for 20 minutes, the composite is poured into a mold. The results of the tests show that the composite containing bismuth performs better than the composite without bismuth. Due to the presence of bismuth at the interface between the particle and the matrix, proper adhesion is achieved. Also, due to the reduction in the surface tension of the melt due to the addition of bismuth, more particles are created with a more uniform distribution in the matrix.

Description

Description of the invention Title of the invention (as stated in the declaration) Method for manufacturing A356 / SiC aluminum matrix composite with bismuth Technical background of the relevant invention This invention is related to the field of materials engineering and manufacturing and can provide the manufacture of aluminum matrix composites without increasing production steps and costs and with greater efficiency. Technical problem and stating the objectives of the invention Aluminum matrix composites, in which aluminum alloys such as A356 form the matrix phase, are generally strengthened by adding ceramic reinforcing materials such as SiC, Al2O3, B4C, ZrO2, TiB2. However, due to the ceramic nature of the reinforcing particles, aluminum composites face problems in terms of wettability and non-uniform particle distribution, as well as poor bonding at the matrix / particle interface. These factors lead to lack of cohesion in the structure and, as a result, a decrease in the properties of the produced composite. In order to increase the wettability of the particles and create a stronger matrix / particle interface, methods such as particle preheating, coating, mechanical alloying, and ultrasonic waves have been used. However, in addition to increasing the number of processes and production cost, the aforementioned methods have not been able to completely solve the problem of wettability and proper distribution of particles in the composite structure. The purpose of this invention is to provide a method for manufacturing an aluminum matrix composite that improves the bonding of the matrix and the reinforcement, thereby increasing the performance of the composite, without increasing the production steps and manufacturing costs. A description of the state of the prior art and the history of developments related to the claimed invention. Compared to methods such as powder metallurgy, milling, penetration and friction stir welding, vortex is a cheaper and easier method for producing aluminum matrix composites. Compo-casting is a type of stirring method in which particles are added to the matrix alloy while it is in a semi-solid state. It has been reported that the compo-casting process produces a composite with better properties due to the better wettability of the reinforcing particles by the matrix (Sajjadi et al., 2012, “Comparison of microstructure and mechanical properties of A356 aluminum alloy / Al2O3 composites fabricated by stir and compo-casting processes,” Materials & Design, and Tahman et al., 2013, “Fabrication of Al / A206–Al2O3nano / micro composite by combining ball milling and stir casting technology,” Materials & Design). However, it is generally difficult to obtain a good bond between ceramic particles and the aluminum matrix due to the low wettability. Preheating the reinforcing particles at high temperature (Abbaspour et al., 2010, in an article titled Compocasting of A356-CNT composite in the journal Transactions of the Nonferrous Metal Society of China), milling (Dehghan and Shahmiri, 2012, in an article titled Production of A356–1wt% SiC nanocomposite by the modified stir casting method in the journal Materials Science and Engineering A), and coating the particles (Singh and Balasubramanian, 2009, in an article titled Processing and properties of copper-coated carbon fiber reinforced aluminum alloy composites in the journal Materials Processing Technology) are the most important methods that have been used to increase the wettability in molten aluminum. Another method is to treat the melt and add elements that reduce the surface tension of molten aluminum.Singh et al. (2014) investigated the effects of magnesium addition on the mechanical properties of Al-SiC composites (Enhancement of wettability of aluminum-based silicon carbide reinforced particulate metal matrix composite in the journal High Temperature Materials and Processes). The authors reported improvements in tensile strength and hardness with increasing reinforcement content. Although magnesium was introduced as a surface activating element in this paper, it was not the case that Pai et al. (1995) (Role of magnesium in cast aluminum alloy matrix composites in the journal Materials Science) reported that magnesium addition reduced melt fluidity and increased particle agglomeration at SiC contents above 15%.Also, Mohammadpour and his colleagues in 2014 investigated the addition of magnesium, calcium, silicon, titanium, zinc and zirconium and reported the best results for magnesium and then calcium (article titled Effect of interfacial-active elements addition on the incorporation of micron-sized SiC particles in molten pure aluminum in the journal Ceramics International). In 2016, in an article titled Fabrication of aluminum matrix composites reinforced with nano- to micrometer-sized SiC particles in the journal Materials & Design, Mousavian and his colleagues produced Al-SiC composites by stirring method, while SiC reinforcing particles were milled with chromium, copper and titanium before entering the melt. These elements have been introduced as factors to improve wettability. Their results showed that titanium successfully caused proper particle distribution and improved composite properties, while chromium and copper led to a decrease in mechanical properties. In patent number 64183 in 2009, Mahdavi and Ekhlaqi produced a powder mixture with graphite to produce Al-SiC composite. It has been claimed that the lack of formation of metal oxides during powder production and the absence of destructive reactions at the matrix-reinforcement interface improves tribological properties. Niroumand and Amirkhanloo in patent number 68402 in 2010 claimed that adding magnesium in the form of Al-SiC-Mg composite powder results in the desired structure and maximum mechanical properties in the production of aluminum composites. Lee et al., in patent number JP2016113696A in 2016, described the use of nitrogen gas to produce aluminum composites. In patent number WO2015104613A1 in 2014, Tejada and Garcia disclosed a method for producing aluminum matrix composites that requires coating of reinforcing particles and forging operations on the casting. The advantage of using electroless coatings on composite reinforcing particles is described in patent number KR20160022281A in 2016 by Kim et al. In patent number IN202141012155 in 2021, Kumar et al. introduced a powder metallurgy method for producing graphene-reinforced aluminum composites that were thermally prepared. The use of mechanical force has also been considered by the inventors. In patent number CN112195358 in 2020, Yiwang and his colleagues claimed that the use of ultrasonic vibration process has a positive effect on the manufacturing of composites.Xiumin et al., in patent number CN104726734 in 2016, used ball milling and powder mixing under argon gas to produce Al-SiC composite. In 2013, Akbari and colleagues used milling of aluminum powder with copper to improve the cohesion and properties of A356-Al2O3 aluminum composite (article titled Fabrication of nano-sized Al2O3reinforced casting aluminum composite focusing on preparation process of reinforcement powders and evaluation of its properties in the journal Composites Part B: Engineering). They also suggested that the gradual oxidation of the metal powders may have a negative effect on improving the composite properties. In 2018, Yuan and colleagues used pressure casting to reinforce A356 alloy with SiC (article titled Preparation and properties of nano-SiC p / A356 composites synthesized with a new process in the journal Materials Science and Technology). The authors stated that when the particle size is too small, the stirring process does not disperse the particles as well as expected and agglomeration of the particles occurs. In 2020, Panthglin et al. investigated the effect of adding zirconium to A356-SiC composite without adding additional magnesium and reported that the addition of zirconium resulted in more particle placement and better distribution (article titled The Effects of Zr Addition on the Microstructure and Mechanical Properties of A356–SiC Composites in the International Journal of Metalcasting). The results presented were different from the findings of Mohammadpour et al. in 2014. The effect of bismuth on the properties of molten aluminum was investigated by Koike et al. in 2000 (article titled Effects of the liquid phase on tensile elongation of Al–Bi alloy in the journal Materials Science and Engineering A). Their results showed that bismuth reduces the surface tension of molten aluminum. So far, various researches have been presented in the field of manufacturing aluminum composites, and based on these researches, practical and valuable methods have been presented. Some of these methods face limitations due to the number of processes required or the complexity of the process in terms of implementation. Therefore, ease of production and low cost are significant conditions for composite production. The purpose of this invention is to present a practical method for manufacturing aluminum composites that, in addition to reducing production steps, improves the continuity of the matrix / particle interface and creates a more appropriate distribution of reinforcing particles within the matrix. The manufacturing process, in addition to facilitating manufacturing, also improves the performance of the composite. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention This invention is a method for solving the problem of wettability of reinforcing particles in an aluminum matrix by adding bismuth. Bismuth reduces the surface tension of the melt, resulting in better melt inclusion of reinforcing particles. Also, due to its low melting point, bismuth is located at the matrix / reinforcement interface in the final stages of solidification, reducing the discontinuity between the matrix and the particle. In order to increase efficiency, the manufacturing process is carried out in the compositing mode. The process used in this invention is shown in a flowchart in Figure 1. The method presented in this invention consists of 4 steps, which are explained below. 1- Thermal analysis Figure 2 shows a schematic of how the thermal analysis of the cooling curve was performed. The A356 alloy with the chemical composition Al-7%Si-0.35%Mg was melted in an electric furnace and poured into a mold that had been preheated to 750 °C for 15 min. The temperature-time data were transmitted and recorded to a data logger and then to a computer using a type K thermocouple placed in the center of the mold. 2- Determining the composting temperature Using the recorded data from thermal analysis, a temperature-solid fraction curve was drawn, which is shown in Figure 3. The temperature of 605°C, corresponding to a solid fraction of less than 20%, was chosen as the temperature for the composite manufacturing process using the compocasting method. 3- Adding bismuth and mechanical stirring Figure 4 shows a schematic of the mechanical stirrer used to make the composite. First, 1 wt% pure bismuth (99.99%) and then 5 wt% SiC with a size of 25 to 75 μm were slowly added under the melt and stirred at a speed of 600 rpm for 20 minutes at a temperature of 605 °C. In order to investigate the effect of bismuth and compare the results of the composite without bismuth and with bismuth, the composite manufacturing process was repeated without adding bismuth. 4- Control experiments In order to evaluate the manufacturing process and investigate the effect of bismuth addition on the performance of the produced composite, SEM analysis, mechanical property tests including tensile and hardness tests, as well as abrasion tests were performed. The results obtained from these tests are presented below. SEM images Figure 5 shows SEM images of composite samples without bismuth (5-a and 5-b) and with bismuth (5-c and 5-d). In the composite without bismuth, the distribution of SiC particles is heterogeneous and the particles are stuck together and agglomerated. Also, discontinuity is created near the matrix / particle interface. In the composite containing bismuth, the particle distribution is more appropriate and much less agglomeration is observed. Also, compared to the sample without bismuth, a larger number of SiC particles are included inside the matrix. Figure 6 shows the linear elemental analysis that bismuth particles are identified at the matrix-particle interface. Bismuth has created a good connection between the matrix and the particle. Figure 7 shows the SEM image of the composite sample containing bismuth, which has been removed by HCl solution in order to better examine the aluminum matrix. This figure also confirms the presence of bismuth (white areas) around the SiC particles. Tensile test In order to evaluate the tensile properties, uniaxial tensile test was performed using Instron-5982 machine and based on ASTM E8 standard at ambient temperature, and the stress-strain curve and the results obtained from it are presented in Figure 8-a and 8-b, respectively. The ultimate tensile strength of the composite without bismuth is 117.25 MPa, which has increased to 153.75 MPa with the addition of bismuth. Also, the percentage of elongation of the composite has increased by 44% after the addition of bismuth. Hardness test The changes in hardness are shown in Figure 8-b. The hardness of the composite without bismuth is 3.70 Brinell, which increases to 4.78 Brinell after the addition of bismuth. Fractography The fracture surface of the tensile specimens is shown in Figure 9. The fracture surface of the composite without bismuth consists of agglomerated particles. In the composite containing bismuth, SiC is well surrounded by the matrix and good cohesion between the particles and the matrix is ​​observed. Abrasion test One of the most important properties of composites is wear resistance, which was measured by the pin-on-disk test according to ASTM-G99-05 using a Ducom-TR20-LE machine on 25 mm long and 6 mm diameter pins prepared by machining. The weight loss changes under loads of 5 and 20 N are shown in Figures 10-a and 10-b. Adding bismuth to the composite reduces the weight loss by 22.5% and 37% under loads of 5 and 20 N, respectively. The reduction in wear rate and improvement in wear resistance of the composite containing bismuth can be seen from Figure 11, which shows the changes in wear rate under loads of 5 and 20 N. Figure 12 shows the changes in the friction coefficient of the samples during the wear test. The results show that the friction coefficient of the composite containing bismuth is lower than that of the composite without bismuth. The average coefficient of friction under a load of 5 Newtons for A356 / SiC samples without bismuth and with bismuth is 0.53 and 0.5, respectively. Checking the wear surface For a more detailed examination, the worn surface of the pins was evaluated using SEM, as shown in Figure 13. By adding bismuth, the abrasive wear is transformed into a gentle wear and the grooves become shallower and narrower. The test results showed improved performance of the manufactured composite. Explanation of shapes, maps and diagrams Figure 1: Steps in the composite manufacturing process Figure 2: Schematic of thermal analysis of cooling Figure 3: Temperature-solid fraction curve of the matrix alloy Figure 4: Schematic of mechanical stirring equipment Figure 5: SEM image of the structure of the produced composites (a and b) without and (c and d) with bismuth. Figure 6: Linear element analysis in the common phase of the field and particle Figure 7: SEM image showing the presence of bismuth around the particles Figure 8: (a) Composite stress-strain curves and (b) results extracted from them Figure 9: SEM image of the fracture surface of the composite (a) without and (b) with bismuth. Figure 10: Weight loss during wear test under load of (a) 5 and (b) 20 N Figure 11: Wear rate of composites under 5 and 20 Newton loads Figure 12: Changes in the coefficient of friction of the composite (a and b) without and (c and d) with bismuth under loads of 5 Newtons and 20 Newtons. Figure 13: SEM image of the composite wear surface (a) without and (b) with bismuth A clear and precise statement of the advantages of the claimed invention over prior inventions. The present invention provides an easy method for manufacturing aluminum composite. The advantages of the present invention over previous methods are as follows. Composite production methods require coating of reinforcing particles, preheating of particles, use of inert gas environment, use of ultrasound waves or use of ball mill. These additional processes complicate the production method and increase the cost of composite production, which is a determining factor for industries and production units. The presented method does not require preparation and is an easy process for composite production. Description of at least one implementation method for implementing the invention The present invention can be used as a method for producing aluminum matrix composites with ease of production process. The proposed method in this method is easy to implement and does not require complex equipment. This process can be used to manufacture parts that require wear resistance due to contact with each other, such as piston rods, pistons, cylinder heads, etc. In the inventive method described in the implementation stage, the following steps are performed in order: 1- Preparation of molten A356 and keeping it in a semi-solid state 2- Adding pure bismuth and then SiC to the melt 3- Mechanical stirring of A356 and SiC slurry 4- Casting in mold Explicit mention of the industrial application of the invention In this construction method, the process is simple and practical, and the use of this method is considered and valuable due to the reduction in complexity and cost. Brief description of the invention This invention presents a method for producing an aluminum matrix composite by adding bismuth to the melt. The product of this invention is a composite in which the A356 alloy is reinforced with SiC particles. In order to produce the A356-SiC composite, the A356 melt is created in a resistance furnace, after creating a semi-solid state, first pure bismuth and then SiC reinforcing particles are added. After stirring the melt, the composite is poured into a mold. Due to the presence of bismuth at the interface between the particle and the matrix, proper adhesion is created. Also, due to the reduction in the surface tension of the melt due to the addition of bismuth, more particles are created with a more uniform distribution in the matrix. The results of the experiments indicate the proper performance of the composite containing bismuth compared to the composite without bismuth.

Claims

Complaint What is claimed: Claim 1) A method for manufacturing an A356 / SiC aluminum matrix composite was presented. First, 1 wt% bismuth and then 5 wt% SiC particles were added to the melt in a semi-solid state at a temperature of 605°C and mechanically stirred for 20 minutes at a speed of 600 rpm.

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