Proceeding ICST (2021)

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ICST conference, December 14th 2020, published online: June 1st 2021 56

Mechanical characterization of powder metallurgy products

with aluminum waste materials using multi stage pressing

method

I Made Mara, IGAK Chatur Adhi W, Made Wijana, I Made Nuarsa, AA Alit Triadi *

Mechanical Engineering, Engineering Faculty, Mataram University

Author Email :_{[email protected] , [email protected],}

[email protected] , [email protected] , *Corresponding author: [email protected]

Abstract.Products resulting from the powder metallurgy process are increasingly competitive because they have advantages in terms of their mechanical and physical properties. Material engineering by mixing several types of metal powders is possible. The composition of this powder metallurgy process material is a mixture of aluminum powder (80%), copper powder (15%) and silicon carbide powder (5%) by weight, and then the compaction is carried out with a pressure of 3, 4 and 5 metric tons gradually with heating temperature of 125oC. Sintering in the furnace at temperature variations of 450oC, 500oC and 550oC and the sintering time is 60 minutes. The tests carried out are the compressive strength test by the Universal Testing Machine (UTM) and the hardness test using the Rockwell method (HRF). The highest compressive strength of 120 MPa was obtained at sintering temperature of 450oCwith one-stage compaction. In addition, the highest hardness of 80 HRF was obtained at sintering temperature of 450oC with one-stage compaction. Multi stage compaction provides lower compressive strength and hardness than single-stage compaction (compressive strength of 110 MPa and hardness of 77 HRF at sintering temperature of 450oC). The higher the sintering temperature, the lower the compressive strength and hardness of the specimen, both in single-stage and multi-single-stage compaction. Those, it can be concluded that the multi single-stage pressing method reduces mechanical properties and also requires a longer processing time.

Keywords: Aluminum; compressive strength; hardness; powder metallurgy

1. Introduction

In Indonesia, there are many large and small industries established, in the effort to develop technology, many efforts must be made, namely by creating new works that are low cost, have high efficiency and are economical. However, the utilization and knowledge of how to process it is still lacking, so that a lot of material is wasted. So that is required to be creative through thoughts or ideas. One of them is by

Proceeding ICST (2021)

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using used metal materials or growls to be made into metal powders. Metal powder can be processed into products through a pressing (compacting) process with the help of a heating device into solid metal objects. Powder metallurgy is the process of making powder and finished objects from metal powders or metal alloys with a certain powder size without going through the process of smelting. The energy used in this process is relatively low, while other advantages include that the final product can be directly adjusted to the desired dimensions, which means that it will reduce machining costs and wasted raw materials. The main problem in utilizing the results of the powder is the best possible treatment of the metal powder, so that it becomes an object that has a high value [1].

To get the perfect compaction process, the compacting process can be carried out at high temperatures or known as Hot Pressing. Press when hot will make the powder softer / plastic, making it easier to compact. For this reason, the effect of heating temperature must be controlled in order to obtain a homogeneous product. Density is very influential on the strength of the product produced. The particle size, shape and size distribution of metal powders affect the characteristics and physical properties of the object being compressed. The powder is made according to specifications including: shape, fineness, particle size distribution, flow ability, chemical properties, compressibility, apparent density and sinter properties. The shape of the powder particles depending on the method of manufacture, can be feathery, irregular, dendritic, flat or sharp angled. Fineness is closely related to grain size and is determined by sieving the powder with a standard sieve or by microscopic measurements. Standard sieves with mesh sizes of 36 to 850 µm were used to check the size and determine the particle size distribution in a particular area. the Cu particle size has a significant impact on the physical and mechanical properties of the CuSnFeNi/diamond composites. The smaller the Cu particle size, the larger thermal conductivity, the hardness, and flexural strength are obtained [2].

The particle size distribution is determined based on the number of particles of each standard size in the powder. The distribution effect on flow ability, apparent density and product porosity is quite large. The distribution cannot be changed without affecting the size of the compressed object. Flow ability is a characteristic that describes the powder flow properties and the ability to fill the print space [3]. Can be described as the flow rate through a certain gap. Chemical properties concern powder purity, allowable amount of oxide and content of other elements. Compressibility is the ratio of the volume of the original powder to the volume of the object being pressed. This value varies and is influenced by the distribution of grain size and shape. The raw compressive strength depends on compressibility. Bulk density or clear weight of powder is expressed in kilograms per cubic meter. This price must be fixed, so that the amount of powder that fills the mold each time remains the same. Sinter is the process of binding particles through a heating process [4].

2. Experiment method

2.1. Materials

The material that will be used in this research is aluminum waste (material for shelves, frames). Furthermore, the material is made into powder by grinding and then sieving. The size of aluminum powder used was 170 µm. Added fine powder of other materials, namely Cu and SiC, with a composition of 80% Al, 15% Cu and 5% SiC by mass. The ingredients are mixed using a magnetic stirrer in dry conditions. Furthermore, the specimen is made. In the specimen-making process, compaction loading of 3000, 4000 and 5000 kg is carried out gradually with a low heating temperature of 1250C.

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In the specimen-making process, compaction loading of 3000, 4000 and 5000 kg is carried out gradually with a low heating temperature of 1250C (figure 1a). After the compacting process, the specimens were sintered in the kitchen with several temperature variations, namely 4500C, 5000C and 5500C. The sintering process time is 60 minutes (figure 1b). After the sintering process is complete, the specimens are removed from the kitchen by air cooling. The test carried out on the specimen are a hardness test using the Rockwell method (HRF) and a compressive strength by Universal Testing Machine (UTM).

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Figure 1. a) Compaction, b) Sintering

2.2. Testing

The test carried out is the hardness test using the Rockwell method by first grinding the specimens on a polishing machine using rubbing paper / sandpaper. Rubbing paper with a slightly coarse grade (grade 350), then grade 500, 800 and 1000. Regulating the pressure load used in the hardness test equipment is a load of 60 kgf. The indentation of each specimen is three points with each variation being repeated three times. The specimen is shaped like a coin, with flat sides. The dimensions of the coins with a diameter of 18 mm and a thickness of 10 mm are shown in Figure 2a.

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Figure 2. a) Specimen, b) Hardness test

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hours in a standard test atmosphere of 290C and a relative humidity of 64%. The specimen has a height and diameter of 1 cm x 1 cm [5]. Shown in Figure 3.

Figure 3. Universal Testing Machine (UTM) for press testing

3. Result and discussion

3.1. Microstructure analysis of Al, Cu and SiC powders

Figures 3a, 3b, and 4 show photos of the microstructure of the powder raw materials Al, Cu, and SiC. The microstructure photo of the Al powder (white color) shows a large number of pores (black color) as shown in Figure 3a. A number of pores were also seen in Cu and SiC powders as shown in Figures 3b and 4. The presence of a large number of pores is thought to be related to the density of each powder [6]. The density of a material will be low when the porosity of the material is high. The porosity present in the material is in the least condition or it can be said that the bond between the surface of the particles is in the best condition. This also answers the reason why the amount of porosity of the Al powder is higher than the other two powdered materials, because the density of Cu powder is lower than the other two materials. The structural photo of the SiC powder as shown in Figure 4 was found to have fewer pores than the other two materials, this was due to the strong and hard SiC powder.

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Figure 4. Silicon carbide (SiC) powder, magnification 40 x

3.2 Hardness analysis of Al / Cu / SiC mixture

The hardness of pure aluminum waste material (without a mixture of Cu and SiC) has an average value of 35 HRF with a purity level of 87.5% and the rest is in the form of metal oxides at 1 stage compaction. 1-stage compaction means direct loading of 5000 kg and held for 4 minutes. While the 3-stage compaction means the gradual loading of 3000 kg, 4000 kg and 5000 kg and each 3-stage is held for 3 minutes.

The hardness value is shown in Figure 5. The hardness value of the specimens with 1-stage compacting was higher than the 3-stage compaction (but not too significant). This condition could be due to the direct compression process leading to better homogeneity (smaller porosity). The hardness value of the Al / Cu / SiC material is shown in Figure 5. The value of the hardness of the material increases in the sintering temperature range of 4500C compared to materials with sintering at 5500C. The highest hardness value was obtained from the material at 4500C sintering temperature of 80 HRF, then followed by the Al / Cu / SiC material at 5000C and 5500C, 74 HRF and 52 HRF, respectively. This increase is thought to have occurred because the particles of metal powders were bound to each other in a solid condition due to compaction and heating, so that the hardness of the material was high. The maximum hardness of aluminum of 47 BHN was obtained at the optimum compacting pressure between 162 Mpa to 170 Mpa, the optimum sintering temperature of 5000C and the sintering time between 40 to 50 minutes. In the manufacture of glide bearing products with Al and 5% graphite alloy materials, it was found that the maximum hardness was obtained at a compacting pressure of 600 MPa with a holding time of 180 minutes, namely 54.5 kg / mm2 [4,5]. The results of the same study but different materials have also been reported and stated that the interaction between copper tungsten particles is strong due to compaction and sintering [7].

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Figure 5. Material hardness in single and multi-stage compacting and sintering temperature variations

3.3. Compressive strength

Figure 6 shows that at 450oC of sintering temperature, the compressive strength of the material is the highest compared to the sintering temperature of 500oC and 550oC where the compressive strength is 120 MPa, both in direct and multi-stage compaction.

The increase in the compressive strength indicates that the sintering temperature has an effect on the compressive strength of the Al/Cu/SiC material. The interface bond between the aluminum-copper-silicon carbide powder is formed relatively strong to produce a high compressive strength. The presence of the element SiC in metals contributes to the strength and hardness of metallic materials [7]. The results of the same study with the same material but different at the time of compacting (without heating) stated that the sintering temperature had an effect on hardness [8].

Figure 5. Material compressive strength 4. Conclusions

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increasing of sintering temperature, both in direct and multi-stage compaction. This is caused by the release of SiC from other particles, thereby reducing the hardness of the material.

Acknowledgement

The author would like to thank the University of Mataram on the Competitive Grant financed research. References

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