Heat Treatment Of Aluminium And Its Alloys Pdf

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Heat treatment processes, namely, annealing, normalizing, quenching, and tempering, are carried out on the alloy samples.

These materials exhibit medium strength and ductility at room temperature and can be strengthened by aging treatment.

The optimisation of heat treatment parameters for Al—Cu— Mg—Ag cast alloys 2xxx having different microstructural scales was investigated. Thermo-Calc software was used to design optimal alloy compositions. Differential scanning calorimetry DSC , scanning electron microscopy and wavelength-dispersive spectroscopy technique were employed to determine proper solution heat treatment temperature and homogenisation time as well as incidence of incipient melting. Proper artificial ageing temperature for each alloy was identified using DSC analysis and hardness measurement. Addition of Mg to Al—Cu alloys promoted the formation of phases having a rather low melting temperature which demands multi-step solution treatment.

Effects of Heat Treatment on the Mechanical Properties of Al-4% Ti Alloy

The optimisation of heat treatment parameters for Al—Cu— Mg—Ag cast alloys 2xxx having different microstructural scales was investigated. Thermo-Calc software was used to design optimal alloy compositions. Differential scanning calorimetry DSC , scanning electron microscopy and wavelength-dispersive spectroscopy technique were employed to determine proper solution heat treatment temperature and homogenisation time as well as incidence of incipient melting.

Proper artificial ageing temperature for each alloy was identified using DSC analysis and hardness measurement. Addition of Mg to Al—Cu alloys promoted the formation of phases having a rather low melting temperature which demands multi-step solution treatment. Presence of Ag decreases the melting temperature of intermetallics beside Al 2 Cu and improvement in age-hardening response. Peak-aged temperature is primarily affected by the chemical composition rather than the microstructural scale.

Replacement of these alloys with ferrous components in the vehicle power trains e. Addition of Cu and Mg to Al strengthens the alloy not only through a solid solution strengthening but also in substantial dispersion strengthening mechanism through the formation of Al 2 Cu and Al 2 CuMg phases by heat treatment [ 4 ].

On the other hand, elevated solution temperature and prolonged SHT result in the occurring of incipient melting of phases and wasting of energy, respectively [ 10 ]. Incipient melting harms mechanical properties, and therefore, it is crucial to choose the optimal SHT for sound microstructure and desired performance. Solution temperature controls the diffusion-based dissolution rate of Al 2 Cu, while homogenisation time is primarily determined by diffusion distance [ 11 ].

Factors such as fraction, type and morphology of Al 2 Cu phases also determine their dissolution rate [ 12 , 13 ]. Masuku et al. Moller et al. Daswa et al. In order to transform the supersaturated solid solution structure solution heat-treated to the high-strength tempers characterised by strengthening precipitates, the temperature of artificial ageing is the key parameter.

At the optimal ageing temperature, the alloy reaches the peak-ageing hardness value within an adequate time, while, on the other hand, lower temperatures require a relatively long time to reach the peak; at higher temperatures, precipitates turn into relatively large non-coherent particles offering low strength over-aged [ 18 ]. The peak-ageing temperature was changed by changes in concentration of Cu, Mg and Ag in the alloy [ 20 ].

Li et al. The solidification of cast components is a complex process where factors such as casting technology e. The cooling rate varies with the local thickness of the cast component: a high cooling rate results in a refined microstructural features, while lower cooling rates yield a coarser microstructure [ 13 ]. It was shown that the microstructural scale coarseness of microstructure in Al—Si alloys influences solution treatment mechanism [ 10 ] and artificial ageing response [ 25 ].

Refined particles require a significantly shorter time to dissolve rather than the coarse ones. Unlike heat treatment of Al—Si cast alloys, no detailed discussion about heat treatment of Al—Cu— Mg—Ag alloys is reported in the literature. Since the as-cast microstructural scale controls mechanical properties of castings [ 24 ], it is, therefore, a useful exercise to investigate the role of microstructural scale on solution heat treatment and artificial ageing of Al—Cu— Mg—Ag cast alloys.

The main aim of the present study is to identify proper temperature range and time for solution heat treatment and artificial ageing of Al—Cu— Mg—Ag alloys having different as-cast microstructural scales using differential scanning calorimetry analysis, microstructural characterisation and hardness testing. The role of Mg and Ag addition, as well as variation in microstructural scale on SHT and artificial ageing, was discussed.

Three different Al—Cu-based alloys were produced by melting pure Al ingots No degassing treatment was applied during the melting process. The furnace was mounted on a motorised lifting device, while the rods are in a stationary position. After the rods had been re-melted, the furnace was raised at a prescribed speed.

The pulling speed of the furnace controls the solidification rate. In order to produce cast specimens with different microstructural scales, the pulling speed of the furnace was set to 0.

Three tests were performed for each condition. Three different specimens were investigated for each condition. Olympus image analyser was used to coordinate the measured point with respect to distance to the nearest particle Fig.

Thereafter, they are artificially aged in Heraeus D furnace. The temperature of specimens was controlled using thermocouples inserted into each specimen during SHT and artificial ageing processes. The methodology of the heat treatment was based on choosing the temperature of SHT and artificial ageing with respect to onset temperature of melting of intermetallics and precipitates formation, respectively. The onset temperatures were identified through DSC analysis. In the case of incomplete dissolution of intermetallics, SHT was carried out at relatively higher temperature.

In the presence of peaks corresponding to melting of intermetallic compounds having lower melting temperature compared to Al 2 Cu, two-step SHT was applied in order to prevent occurring of incipient melting of phases with lower melting temperatures. Temperature of artificial ageing was chosen with respect to onset temperature of precipitates formation in order to find the temperature which gives the peak of hardness within the adequate time.

For each condition, five measurements in identical locations from cylindrical sections were taken from three distinct specimens. The hardness of the alloys was measured both in as-cast and in heat-treated conditions. The average hardness was calculated and plotted with respect to ageing time.

Increasing Cu concentration generally results in a higher fraction of Al 2 Cu. Although increasing Cu up to 5. Solution temperatures closer to liquidus temperature burden the complete dissolution of Al 2 Cu with low risk of incipient melting.

In fact, a certain gap between SHT temperature and liquidus line should be maintained. Introducing Mg to Al—Cu system enhances the response to ageing due to complex interactions between Mg atoms and vacancies [ 27 ]. Although high Mg level in the alloy is desired to intensify hardenability, it brings some difficulties for the SHT.

Moreover, generation of Mg-bearing intermetallic of S-Al 2 CuMg which has a relatively lower melting temperature requires multi-step SHT to prevent overburning of such phase [ 28 ]. Solidification simulation based on both equilibrium condition and Scheil equation showed that addition of only 0. Equilibrium condition basically simulates solidification under very slow rate, while the Scheil equation is valid when the contribution from back diffusion is negligible [ 10 ] Fig. Two alloys of Al—4.

Evidence in the studies showed a range of 0. Based on solidification simulation, Ag incorporation of 0. Bai et al. In another study, where a varied set of compositions was studied to optimise precipitation hardening, the addition of 0.

In the present study, according to the findings in other works, the addition of 0. Limited traces of elongated Fe-rich intermetallics were also identified in the as-cast microstructures of all alloys, known as Al 7 Cu 2 Fe [ 33 ].

Solidification rates represent fine, medium and coarse microstructural scale, respectively. Solidification rate determines the microstructural scale also known as the coarseness of microstructure. Increasing the solidification rate from 0. A continuous distribution of Al 2 Cu particles was observed, from a few hundreds of microns to below fifty microns in length. The average concentration of Cu in the matrix for Al—Cu alloy was lower for the case of high solidification rate fine microstructural scale compared to low ones medium and coarse microstructural scales.

Mg solute concentration, however, was found to be relatively higher in fine microstructure compared to coarser microstructure.

Although Al 2 Cu phase was identified in two different forms of eutectic and blocky phase Fig. Typical DSC heating curves of as-cast alloys cast under different solidification rates different microstructural scales. The curves have been offset for clarity. Some specimens of both medium and coarse microstructure showed double peaks peak 1 and 2 , and others showed triple peaks peaks 1, 2 and 3.

Although these phases could not be identified using microscopic characterisation tools, DSC curve revealed their attendance. Solidification simulations based on thermodynamic calculations also revealed the presence of 1. In fact, it seems that high cooling rate arrested the formation of S-Al 2 CuMg phase in compositions of both Al—4. According to equilibrium binary Al—Cu phase diagram Fig.

This is primarily attributed to different microstructural scales. In medium and coarse microstructure, solute concentration did not reach 4. Considerable fraction of residual Al 2 Cu was observed in medium microstructure, while negligible particles remained undissolved in the fine microstructure, which agrees with the higher solute concentration in the fine microstructure. Han et al. The author pointed out in another work that size and morphology of Al 2 Cu phase influence dissolution rate where fine particles with lower aspect ratio dissolve faster than coarse elongated one [ 13 ].

Liu et al. This was similarly observed for Al—Cu—Mg and Al—Cu—Mg—Ag alloys, since the larger average diffusion distance in the coarse microstructure requires a reasonably long time for reaching a homogeneous distribution of Cu solutes. Albeit the magnitude of peaks significantly differed as a function of microstructural scale, the area under peaks of DSC curve with respect to a calorimetric constant is proportional to the enthalpy of the phase transformation.

Therefore, a fast dissolution rate of Al 2 Cu in fine microstructure is consistent with a lowered enthalpy of dissolution. In fact, refined continuous particles can be dissolved exchanging lower heat rather than coarser particles and elongated Al 2 Cu networks.

Therefore, proper dissolution temperature seems to be primarily influenced by the area under the peak rather than the onset temperature of the peaks. This is due to the immediate effect of SHT temperature on the diffusion rate which is magnified by raising the temperature [ 11 ].

The Cu solute levels in solution-treated condition reached 4. According to the equilibrium phase diagram, Cu has a maximum solubility of 4. It means that Cu solute level in the alloy by applying single-step solution treatment might have not reached the maximum concentration value.

However, complex solution treatments for similar alloys proposed in scholars, such as controlled heating [ 17 ] or multi-step solubilisation and homogenisation treatment [ 16 ], may assist in reaching solute levels closer to equilibrium values.

Three distinct endothermic peaks, which represent the melting of Al 2 Cu and AlCuMg phases, in the as-cast condition disappeared in the solution-treated condition. This is a further confirmation of fairly complete dissolution of such phases, which was also pointed out elsewhere [ 15 ].

The alloy is Al—Cu—Mg with medium microstructural scale. Solid lines represent the linear trends of the concentration points. This finding was pointed out elsewhere [ 35 ]. An appreciable increase in Cu solute level was realised after 2-h SHT.

Aluminium alloy

Aluminium alloys or aluminum alloys ; see spelling differences are alloys in which aluminium Al is the predominant metal. The typical alloying elements are copper , magnesium , manganese , silicon , tin and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminium alloy system is Al—Si , where the high levels of silicon 4. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed mostly of aluminium have been very important in aerospace manufacturing since the introduction of metal-skinned aircraft.

Types of Aluminum Heat Treatments

Aluminum heat treatment is a process by which the strength and hardness of a specific subset of aluminum alloys, namely the wrought and cast alloys that are precipitation hardenable, are increased. In addition, annealing may be required for parts that have experienced strain hardening during their forming process. The typical aluminum heat treatments are annealing, homogenizing, solution heat treatment, natural aging, and artificial aging also known as precipitation hardening. It is important to keep in mind that the heat treating of aluminum is quite different from steel.

They are both widely used in welding fabrication and have somewhat different characteristics associated with their chemical and metallurgical structure and their reactions during the arc welding process. In order to best answer your question, we first need to understand the basic differences between these two groups of alloys. Non-Heat-Treatable Aluminum Alloys - The strength of these alloys is initially produced by alloying the aluminum with additions of other elements. These alloys consist of the pure aluminum alloys 1xxx series , manganese alloys 3xxx series , silicon alloys 4xxx series and magnesium alloys 5xxx series. A further increase in strength of these alloys is obtained through various degrees of cold working or strain hardening.

Effects of Heat Treatment on the Mechanical Properties of Al-4% Ti Alloy

Regret for the inconvenience: we are taking measures to prevent fraudulent form submissions by extractors and page crawlers. Received: February 16, Published: April 20, DOI: Download PDF. The intention of authoring this paper was giving the report of reviewing task of the previous researches done on the strengthening mechanisms and heat treatment of 7xxx aluminum alloys. The overall conclusion is that, the most powerful and so the most common strengthening mechanism in 7xxx alloys is the precipitation hardening T6 heat treatment. On the other hand, stress corrosion is a problem in T6 treated 7xxx alloys, to address which, researchers have turned to special heat treatment called RRA retrogression and re-aging which picks the strength from T6, and stress corrosion resistance from T7x heat treatments.

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1 Response
  1. Carlos R.

    PDF | Aluminum alloy has an extensive range of industrial application due to its consistent mechanical properties and structural integrity. The heat | Find, read.

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