Isothermal Soaking Time Research Articles

The Effect of Soaking Time on Mechanical Properties of Roll-Bonded AA3003 and AA4045 Used for Heat Exchangers

Due to the rising need for energy saving, high-performing automotive heat exchangers, demand has significantly grown in recent years. As a result, effective fin-tube heat exchangers are becoming more popular. These tubes are typically made by rolling flat strips of AA3003 aluminum alloys that have either one or both sides coated with AA4xxx alloys. The AA3003 type of alloy is typically used as the core, which is then covered in either AA4045 or AA4343, which melts during the brazing process to adhere the fins to the tubes. To maintain the optimal size and distribution of manganese (Mn)-containing precipitates, preheating parameters are carefully controlled. Then, longer soaking times or higher soaking temperatures result in larger precipitates, which cause the final product to exhibit poor mechanical properties. Therefore, it is crucial to optimize the different manufacturing steps, such as homogenization, soaking time, and brazing in order to achieve a high quality product. Studies on the impact of homogenization temperature and time on the microstructure of AA3xxx aluminum alloys have been conducted. However, there has been little research on the impact of soaking (reheating) time on AA3003 cladded alloys. Hence, the effects of isothermal soaking time on the microstructure and mechanical properties of AA3003 cladded with AA4045 alloy were investigated in this work. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure and identify intermetallic phases. The final microstructure in terms of grain structure at various homogenization times was characterized by electron backscattered diffraction (EBSD). After the hot-rolling and cold-rolling of the as-received material, large particles of intermetallic (mainly in the form of Chinese script morphology consisting of Fe-Mn-Si) were broken into smaller particles with an increased Fe, Mn, and Si content, indicating the formation of an α-Al(Fe,Mn)Si phase. The α-Al(Mn,Fe)Si was found to be a dominant dispersoid precipitate in the modified AA3003 core. Coarsening of the Al(Mn,Fe)Si dispersoids at 505 °C was only observed at a 45 h homogenization time. The hardness trend with homogenization time was found to be similar to that after homogenization, cold working, and annealing, with exception of an increase in hardness in the latter possibly due to strain hardening (from cold-rolling).

An investigation on SWAAT and electrochemical corrosion behaviour of roll-bonded and brazed aluminium alloy - AA4045/AA3003

The formation of Mn/Fe-containing precipitates during a high-temperature treatment known as homogenization is important for the downstream performance of AA3xxx aluminium alloys. There is currently a significant scientific and industrial interest in the use of Al-Si-Mn-Fe sheet alloys in automotive applications to reduce the weight of vehicles. This work is concerned with the precipitation of dispersoids, which occurs over several hours during heating and holding at the homogenization temperature. In this study, therefore, the effects of isothermal soaking time on the microstructure of AA3003 cladded with AA-045 alloy were investigated. The microstructures and intermetallic phases were analysed using optical microscopy (OM) and scanning electron microscopy (SEM). The seawater acetic acid test (SWAAT) and electrochemical corrosion test were used for studying the corrosion behaviour of the AA4045/AA3003 cladded alloy. The results on the effect of soaking time on both microstructure and corrosion properties of the brazed alloy are presented. The OM results show that the microstructure of these alloys consisted of an Al-Si eutectic phase at the surface of the residual clad and a thick diffusion zone which is a band of dense precipitates ( BDP) between the clad and core. The sheet surface reveals the presence of pitting corrosion on the coupons exposed for 30 days and more. The polarization curves of the corrosion tests show that the AA4045/3003 is susceptible to intergranular corrosion (IGC) as a consequence of the higher amount of grain boundary precipitates formed during the brazing process.

Effect of Municipal Solid Waste Incineration Fly Ash on the Properties, Durability, and Environmental Toxicity of Fired Aluminosilicates

Studies of the effect of fly ash from the incineration of municipal solid wastes on the properties, durability, and environmental toxicity of fired aluminosilicates are presented. In the fabrication of aluminosilicates, fly ash was introduced into the batch in the amounts 2.5 – 7.5%, the firing temperature of the articles was 1000°C, and the isothermal soaking time was 1 h. The investigations showed that the introduction of 2.5% fly ash into aluminosilicates promotes leaching of heavy metals, sulfates, and chlorides according to the current regulation 200333EC. The density of such fired aluminosilicate is equal to 1.8 g/cm3, the strength in compression 24 MPa, water absorption 15.3%, total open porosity 31%, and frost resistance at least 25 freezing-thawing cycles.

Microstructure and mechanical property in a high strength high-Al–low-Si hot-dip galvanized dual phase steel

In this study, two important parameters of heat treatment, namely, cooling rate after intercritical annealing and 460 °C isothermal soaking time, were varied to simulate the hot-dip galvanizing processing in a high-Al–low-Si cold rolling dual phase (DP) steel. The results indicated that after the annealing processes, ferrite and martensite structure were obtained at room temperature for all the heat treatment schedules. The addition of Mn, Cr, Mo to the DP steel and the increase in cooling rate after intercritical annealing increased the hardenability and stability of austenite and decomposition of austenite to ferrite, pearlite and banite was avoided. When the cooling rate was 50 °C/s and at isothermal soaking time was 3 s, the studied steel obtained the best combination of mechanical properties with tensile strength of ∼962 MPa, total elongation of ∼20.5%, and the product of tensile strength and total elongation of ∼19,727 MPa%. The increase in strain hardenability, decrease in ferrite/martensite nanohardness ratio enhanced the ductility of the experimental steel. The refinement of ferrite grain size and increase in ferrite–ferrite grain boundary misorientation led to increase in ductile behavior.

In situ high temperature creep deformation of micro-structure with metal film wire on flexible membrane using geometric phase analysis

A way of measuring the in situ high temperature creep deformation of a micro-structure with a metal film wire on a flexible membrane is developed. The creep deformation measurement of a micro-structure with a Karma alloy wire on a polyimide membrane is used as an application. High temperature gratings were fabricated directly on the surfaces of two Karma alloy wires using the focused ion beam milling technique after the grating frequencies were designed. The grating morphologies with different isothermal soaking time were recorded by a scanning electron microscope with a heating apparatus. The in situ high temperature creep deformations in a micro-region of the structure were measured by performing the geometric phase analysis. The creep behaviors of this structure at 300°C and 500°C were analyzed. The developed measurement method is prospective in evaluating the reliability of the film-wire/substrate structures at a high temperature.

Challenges in hot-dip galvanizing of high strength dual phase steel: Surface selective oxidation and mechanical property degradation

In this work, the two challenges in hot-dip galvanizing of high strength dual phase steel such as surface selective oxidation and mechanical property degradation were discussed. It was shown that the external selective oxidation occurred at low dew point −30°C caused the full coverage of oxides, which is a problem for reactive wetting by molten zinc. Although increase of dew point to +10°C decreased the surface coverage of oxides, the formation of internal oxides consumed the alloying element and accumulated in the subsurface area in a large scale. Furthermore, the heat treatment parameters of hot-dip galvanizing, i.e. cooling rate after inter-critical annealing and the 460°C-isothermal soaking time influenced the mechanical properties.

Cobalt-Chromium Powder Alloys and Retention Coatings Made from Them for Orthopaedic Stomatology

An alloy of Co-Ni-Mo-Cr is prepared by diffusion impregnation with chromium from point sources of cobalt-nickel-molybdenum alloy powder synthesized by combined reduction. Optimum regimes are determined for preparing alloy powder by combined reduction of cobalt, nickel, and molybdenum oxides (reduction temperature 1325 K, isothermal soaking time 3 h) and diffusion impregnation with chromium (temperature 1373 K, isothermal soaking time 4 h). The adhesive strength of a facing coating with material of a dental prosthesis manufactured using the alloy developed is studied. It is shown that with application of retention layers the adhesive strength increases by a factor of three to five compared with using cast spheres (beads).

Features of Carbothermal Synthesis of Aluminum Nitride under Nitrogen Pressure

Aluminum nitride is synthesized by the carbothermal method from a mixture of aluminum oxide and carbon black under a nitrogen pressure of 0.2-0.3 MPa at 1800-1900°C and with an isothermal soaking time of 3 h. The best results are obtained with synthesis at 1800°C and a nitrogen pressure of 0.3 MPa from a charge of stoichiometric composition. Powder with an AlN content up to 99 mass% consists of isometric grains with a narrow size range (2-6 μm). Introduction of lithium carbonate into the original mixture worsens the results.

Crystallization of Y 3Al 5O 12 from an oxynitride glass monitored by high-temperature X-ray diffractometry

It is well established that the glassy phase in a β-SiAlON material, with addition of Y 2O 3, can be crystallized to yttrium aluminium garnet (Y 3Al 5O 12-YAG) by a post-sintering heat treatment. The crystallization of the YAG phase from an oxynitride glass with composition 46·1 wt% Y 2O 3, 26·3 wt% Al 2O 3, 21·6 wt% SiO 2 and wt% Si 3N 4 was studied by means of high-temperature X-ray diffractometry. The kinetics of the crystallization were monitored in terms of the (420)) YAG peak area versus isothermal soaking time at 1150 °C during different heat treatments. The crystallization of the YAG phase was found to proceed as a surface crystallization. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass-ceramics and for heat treatments of YAG/β-SiAlON materials.