The effects of Mg addition on the microstructure and mechanical properties of thixoformed Al–5%Si–Cu alloys

AbstractIn this study, the effects of different amounts of magnesium (Mg) on the microstructures and tensile properties of thixoformed Al–5%Si–Cu alloys were investigated. Three different alloys containing various amounts of Mg (0.5, 0.8 and 1.2wt%) were prepared through the cooling slope casting technique, before they were thixoformed using a compression press. Several of the thixoformed samples were then treated with a T6 heat treatment, that is, solution treatment at 525°C for 8h, quenching in warm water at 60°C, followed by aging at 155°C for 4h. All of the samples were then characterised by optical microscopy (OM), scanning electron microscopy (SEM) energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as by tensile tests. The results revealed that magnesium was able to refine the size of α-Al globules and the eutectic silicon in the samples. It was also observed that a compact π-Al9FeMg3Si5 phase was formed when the magnesium content was 0.8wt% and 1.2wt%. The mechanical properties of the thixoformed alloys improved significantly after the T6 heat treatment. The highest attainment was recorded by the latter alloy (i.e. with 1.2wt%Mg) with its ultimate tensile strength (UTS) as high as 306MPa, yield strength (YS), 264MPa, and elongation to fracture of 1.8%. The fracture of thixoformed alloy with a low Mg content (0.5wt%) showed a combination of dimple and cleavage fracture, whereas in the alloy that contained the highest Mg content (1.2wt%), cleavage fracture was observed

The effects of mg addition on the microstructure and mechanical properties of Thixoformed Al-5%Si-Cu alloys

In this study, the effects of different amounts of magnesium (Mg) on the microstructures and tensile properties of thixoformed Al–5%Si–Cu alloys were investigated. Three different alloys containing various amounts of Mg (0.5, 0.8 and 1.2 wt%) were prepared through the cooling slope casting technique, before they were thixoformed using a compression press. Several of the thixoformed samples were then treated with a T6 heat treatment, that is, solution treatment at 525 C for 8 h, quenching in warm water at 60 C, followed by aging at 155 C for 4 h. All of the samples were then characterised by optical microscopy (OM), scanning electron microscopy (SEM) energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as by tensile tests. The results revealed that magnesium was able to refine the size of a-Al globules and the eutectic silicon in the samples. It was also observed that a compact p-Al9FeMg3Si5 phase was formed when the magnesium content was 0.8 wt% and 1.2 wt%. The mechanical properties of the thixoformed alloys improved significantly after the T6 heat treatment. The highest attainment was recorded by the latter alloy (i.e. with 1.2 wt%Mg) with its ultimate tensile strength (UTS) as high as 306 MPa, yield strength (YS), 264 MPa, and elongation to fracture of 1.8%. The fracture of thixoformed alloy with a low Mg content (0.5 wt%) showed a combination of dimple and cleavage fracture, whereas in the alloy that contained the highest Mg content (1.2 wt%), cleavage fracture was observed

Influence of iron on phase stability and corrosion resistance of Ti-15%Cr alloy

In this study, the effect of Fe addition on the phase stability and corrosion resistance of Ti-15%Cr alloys was investigated. The alloying phenomenon in the specimens was also investigated to determine the effectiveness of the application of pure metallic powders as raw materials for the powder metallurgy method. Ti-15%Cr-1%Fe alloys exhibited needle-like structures within equiaxed structures, while Ti-15%Cr-5%Fe and Ti-15%Cr-10%Fe alloys only showed equiaxed grains. XRD results showed that the β phase could be stabilized by the addition of 5% or more Fe to the alloy. Although the pure powders were used as raw materials, the designated chemical composition, i.e. Ti-15%Cr-(1~10)%Fe can be achieved during sintering. The alloying phenomenon occurred upon sintering due to the high diffusivity of Cr and Fe within the β Ti matrix. The corrosion resistance of the newly developed Ti-15%Cr alloys was significantly improved compared with a commercial Ti-6%Al-4%V alloy

An overview of semisolid processing of aluminium alloys

Semisolid metal processing (SSM) or thixoforming is a new technology that offers several advantages over liquid processing and solid processing. This process utilizes semisolid behavior as well as reduces macrosegregation, porosity, and forming forces during shaping process. A lot of research work has been carried out by various researchers in order to exploit the potential of this process to produce different products especially for automotive industry. This paper will summarise the rheological behavior of aluminium alloys in semisolid slurries, thixoformability of modified aluminium alloys, the effect of feedstock production method on mechanical properties, and the importance of developing low-cost raw materials for semisolid processing

STRESS RELAXATION BEHAVIOUR AND MECHANISM OF HEAT TREATED INCONEL 718 IN HIGH TEMPERATURE ENVIRONMENTS

The stress relaxation behaviour of heat treated nickel-base superalloy Inconel 718 at high temperature was investigated. Solution treatment was applied on the as-received material at 980 oC for 1 hour before water quenching followed by double aging treatments at 720 oC for 8 hours and 621 oC for 8 hours, then cooled in air. The stress relaxation test was conducted at 1 % strain at different test temperatures of 550 oC, 650 oC and 750 oC. The tests were carried out for a total of 72 hours. The tests were interrupted at 3 hours and 48 hours to investigate the evolution of microstructure and changes in material properties by using Scanning Electron Microscope (SEM) and X-Ray Diffractometer (XRD). The results showed that thermal dependent stress increased with decreasing temperature. In contrast, stress relaxation rate increased with increasing temperature. Microstructure observation by SEM showed that recovery process occurred. This was further supported by the decrease in dislocation density with increase in time and temperature, which is in-line with the Vickers micro-hardness results

Thermodynamic modelling of Al-Si-Cu alloys for semisolid processing

Thixoforming is a new method in producing near net shape products which conducted in semisolid condition. This process can reduce macrosegregation, porosity and used low forming forces. Currently there are severals garde of aluminium alloys such as A319, A356 and A357 used in semi-solid metal processing. Therefore there is a demand to widen another grade of aluminium alloys specially tailored for semisolid metal processing. This study discusses the thermodynamic modelling to predict changes in the properties of aluminium alloy A319 expecially when the percentage content of alloying elements such as copper, manganese and iron is varies in order to fulfill the criteria of semisolid metal processing. The termodynamic modelling shows that the solidification temperature decreases from 130 to 113 celcius while the eutectic temperature increase from 510 to 515 celcius when the percentage of copper, mangan and ferum contents is increased. The liquid fraction sensitivity is reduced from 0.017 to 0.007 and teh working window temperature is reduced from 26 to 26 celcius. The results indicate the suitability of these modified alloys as a potential material for semisolid processing

INVESTIGATIONS ON THIXOJOINING PROCESS OF STEEL COMPONENTS

This research is to develop a carbon composite prepared from carbon coir fibers that is reinforced with epoxy resin. Carbon coir fibers were taken from three types of coir fiber specifically designated as CKCF, CYCF and CRCF. The samples were prepared using epoxy resin reinforced with carbon at different weight percentages for three types of coir fiber starting with 0wt.%, 2wt.%, 4wt.%, 6wt.%, 8wt.% and 10wt.%. The mechanical properties such as tensile stress and impact strength were used to characterize all the samples. The morphological study of reinforced samples was also conducted in this research using a SEM machine. The characteristics of all the composite materials were also investigated and discussed. It was determined that the CKCF sample exhibited better mechanical properties than the other coir fiber composites, having a higher average tensile stress value at 11.80MPa and higher impact strength values ranging from 268J to 276J at different carbon content. CKCF with 10wt% AC content had a tremendous impact strength compared with CYCF and CRCF

Ending AIDS as a public health threat by 2030: Time to reset targets for 2025.

Paul De Lay and co-authors introduce a Collection on the design of targets for ending the AIDS epidemic

Permodelan termodinamik aloi al-Si-Cu untuk pemprosesan logam separa pepejal

Pembentukan-tikso merupakan teknologi baharu untuk menghasilkan produk hampir siap dalam keadaan separa pepejal. Proses ini dapat mengurangkan makropengasingan, keliangan serta memerlukan daya pembentukan yang rendah. Sehingga kini, terdapat beberapa aloi aluminium seperti gred A319, A356 dan A357 digunakan untuk pemprosesan logam separa pepejal. Oleh itu, terdapat permintaan untuk mempelbagaikan aloi aluminium daripada gred yang lain untuk pemprosesan logam separa pepejal. Kajian ini membincangkan tentang permodelan termodinamik untuk meramal perubahan sifat aloi aluminium gred A319 apabila kandungan elemen pengaloian seperti tembaga, mangan dan ferum dipelbagaikan agar memenuhi kriteria pemprosesan logam separa pepejal. Kesemua pengiraan dalam kerja permodelan ini menggunakan perisian komersial ‘Java-based Material Properties’ (JMatPro). Pengiraan termodinamik berdasarkan persamaan ‘Scheil’ digunakan untuk menentukan julat suhu pemejalan (ΔT), kepekaan pecahan cecair (dfL/dT) dan suhu tingkap pemprosesan (ΔT30/50). Daripada pengiraan termodinamik, didapati suhu pemejalan aloi yang telah ditingkatkan %bt kandungan tembaga, mangan dan ferum menurun daripada 130 kepada 113°C manakala suhu eutektik meningkat daripada 510 kepada 515°C. Kepekaan pecahan cecair pula berkurangan daripada 0.017 kepada 0.007°C-1 manakala suhu tingkap pemprosesan menurun daripada 26 kepada 24°C. Tindak balas perduaan eutektik pula berlaku antara 30 dan 50% pecahan cecair untuk kesemua kumpulan aloi. Gambarajah fasa digunakan untuk mengetahui fasa sebatian antara logam seperti β-Al5FeSi dan Al2Cu yang terbentuk dalam aloi tersebut. Hasil daripada permodelan termodinamik ini menunjukkan kesesuaian aloi yang dipelbagaikan %bt elemen tembaga, mangan dan ferum digunakan untuk pemprosesan logam separa pepejal

Morphological evolution during partial re-melting of AISI D2 cold-work tool steel

The impact of isothermal temperature and holding time on the microstructural evolution process is studied. This process is used to produce globular microstructures during partial re-melting of AISI D2 cold work tool steel. The experimental results showed that the optimum process factors should be selected according to the criteria for average grain size and shape factor and also by acknowledging the distribution of the liquid phase around the grains. With increasing isothermal temperature and holding time, the liquid phase starts to diffuse into the grain boundaries and spread more evenly. Also, the equiaxed grains were transformed into near-globular shape, which makes the grain size and shape factor more favourable for thixoforming. The work shows that the optimal process condition for the thixoforming of AISI D2 is 1340°C and 5-min holding time, having a shape factor of 1.13 and a particle size of 51 μm