Papers by Keyword: Precipitation Hardening

Abstract: The heat treatable 7xxx series Al alloys (Al-Zn-Mg) show good combination of tensile properties through precipitation hardening. Similar to Al-Cu alloy minor addition of Sn in this alloy also influences its structure and properties. The hardness improves after natural ageing and further improves after duplex ageing. Duplex ageing refines the grains also. SEM-EDX results indicate that β-Sn is present in the form of precipitates. DSC results indicate that Sn suppresses the formation of GP zone and the stability of intermediate η phase is higher.

Abstract: Composite as main materials for ballistic applications has been developed in order to reduce density which leads to lower fuel consumption and faster mobilization. Composite is required to own high hardness and high impact strength for good ballistic performance. Particulate composites Al-7Si-Mg-Zn reinforced by SiC is designed for ballistic applications due to its light weight and high hardness. Whilst the high hardness showed brittle properties, heat treatment process is applied to this composite to reduce it. This research aims to study the effect of magnesium as alloying element to composite Al-7Si-Mg-Zn reinforced by SiC particulate which applied to precipitation hardening. Composites Al-7Si-Zn-SiC with 2, 4 and 6 wt. % Mg is solution treated at 500 oC for 1 hour, followed by ageing at 200 oC. The characterization was carried out by hardness testing, microstructure observations, SEM and EDX observations, impact testing and fractographic observations. Results showed that Mg does not affect hardness of composite by precipitation hardening. Composite with 2, 4, 6 wt. % Mg had 63.83, 62.27, 62.48 HRB on its peak hardness. Mg did not become precipitate in matrix Al-7Si-Mg-Zn because of its low diffusivity in aluminium. Mg worked as wetting agent that reduces interface tension between aluminium matrix and SiC particles in order for composite to own better interface bonding. Therefore impact testing showed significant increase of impact strength with the increase of Mg content. Composite with 2, 4, 6 wt. % Mg had 2075, 3006, 3257 J/mm2 impact strength respectively

Abstract: This work studied the effect of tin (1%Sn) addition in brass 60%Cu+40%Zn (commercial grade) by casting process conducted poured melt metals inside a sand mould and heat treatment in cast brass on microstructure and mechanical properties for solving the cracking of nut and bolt. Three conditions of brass sample for experiment viz.- brass 60%Cu + 40%Zn (commercial grade), brass 60%Cu + 39%Zn+1%Sn (as-cast) and brass 60%Cu+39% Zn+1%Sn (precipitation hardening). The microstructure of specimens all condition, it was found that consists of α phase and β phase. Which brass addition 1% Sn, the β phase content in α phase matrix structure more than brass commercial grade. For microstructure of brass produce by precipitation hardening, shape of α phase are slender and long which have slight distributed in β-phase. The mechanicals properties, that is hardness, ultimate tensile strength and compressive strength. It was found that the brass 60%Cu+39% Zn+1%Sn (precipitation hardening), all test mechanical properties it was higher than the all samples condition. This results can be explain incharacterization of microstructure to gives deformation of copper alloy.

Abstract: The concurrent strengthening process by high-pressure torsion (HPT) and fine precipitation hardening of an Al 6061 alloy has been studied. The HPT was conducted on disks of the alloys at room temperature with an applied pressure of 6 GPa for 1 and 5 turns with a rotation speed of 1 rpm. It is shown that the HPT processing leads to microstructural refinement with an average grain size of ~200 nm and to an increase in hardness up to a saturation after 5 turns. Aging treatment was performed at temperatures of 373 and 423 K for a maximum period up to 256 hours. The hardness at the saturation level remains the same during aging at 373 K. When aged at 423 K, the hardness decreases from the beginning of the aging. This study thus suggests that aging of the HPT-processed sample may not be effective to strengthen the alloy if it is carried out at higher temperatures. It is suggested that simultaneous strengthening may be achieved through reduced straining and aging at reduced temperatures.

Abstract: In this work, an attempt has been made to improve the mechanical strength of 6063 aluminium alloy and thus its lightness via combination of severe plastic deformation (grain size refinement) and heat treatment (precipitation hardening). 6063 aluminium alloy was chosen as the best material for lightweight structures, where mass reduction is important, because of its high extrudability. Samples were hydrostatically extruded (HE) in supersaturated condition and subsequently subjected to an aging process. HE brings about significant grain size refinement well below 1 micron. The influence of aging parameters such as time and temperature on mechanical properties evolution of extruded material was determined. The microstructure of ultrafine grained (UFG) alloy was investigated using transmission electron microscopy. The average grain diameter and grain boundary misorientation angles (using Kikuchi lines) were measured. Mechanical properties were examined in microhardness and tensile tests. The results have shown that it is possible to combine grain boundary and precipitation strengthening and obtain ultrahigh strength in 6xxx series alloys. Additionally, heat treatment of UFG samples causes an increase in ductility measured in tensile tests, which is rather poor in severely deformed materials. To prove advantages of UFG aged samples for lightweight applications, finite element modelling was performed to compare the mass of chair elements made of coarse and ultrafine grained material. Simulations were made for the same stresses applied. It has been shown that if the chair was made of UFG aluminium alloy the mass reduction would be approximately 30 %.

Abstract: Alloys of nominal composition Mg-3Zn-xCa (x = 0, 0.5, 1.0) wt.% were prepared by resistance melting and casting under a protective argon atmosphere. All specimens were examined by hardness tests during ageing at 175 °C. It was shown that calcium addition causes the increase in hardness. A detailed characterisation of microstructure of metastable phases has been carried out using transmission electron microscopy (TEM). Calcium addition resulted in much refined and more homogeneous distribution of the precipitates when compared with the binary Mg-3%Zn alloy. The age-hardening of the ternary alloy is attributed to the fine disc-shape plates lying on the basal plane of the matrix.

Abstract: The essential factors controlling current heat treatment of cast and wrought magnesium alloys are reviewed along with the role of chemical composition and specific elements. The strengthening mechanisms and key precipitates are described, explaining crystallographic limitations of their role within the hcp magnesium matrix. Examples of changing properties are given for conventional alloys with trends in alloy design to magnify the aging effect. Emphasis is placed on magnesium structures produced by semisolid processing routes where a new approach to heat treatment is required.

Abstract: In the research work the precipitation hardening and/or equal channel angular pressing (ECAP) of PM aluminium alloy (AlCuSiMg) samples were investigated. The aim of the research was to determine the optimal parameters for precipitation hardening, especially temperature and time (in terms of maximal strength), and to test the ECAP pressing number for the same properties of precipitation hardened samples. The samples produced were studied by SEM, X-ray diffraction. The results showed that the PM samples had higher mechanical properties after one pressing by ECAP than after precipitation hardening with optimal parameters. In severe plastic deformation a heated die with a channel angle of 90° and ‘A’ route was used. During the heat treatment the applied temperature of the solution treatment was 420-540°C for 1 hour or 3 hours, and hardening was applied at 180°C for 5 hours.

Abstract: Secondary extrusion at 350 °C with the extrusion ratio of 12.25, 25 and 44 was carried out on the Mg-12Gd-3Y-0.5Zr (GW123K) alloy, and the cooling method of the secondary extruded alloys was air cooling and water quenching. Quantitative metallographic analysis method was also employed to study the distribution and volume fraction of dynamic precipitates during the extrusion process. The results showed that secondary extrusion could result in significant grain refinement and the grain size increased with extrusion ratio, which the minimum average grain size was about 5.4μm in the alloy under λ=12.25. The volume fraction of dynamic precipitates decreased with increasing extrusion ratio and the maximum volume fraction was measured to be about 49.2% in the alloy under λ =12.25. Water quenching after extrusion can effectively inhibit dynamic precipitation and the volume fraction of the precipitates ratio decreased from 41.1% after air cooling to 19.6% after water quenching in the same extrusion condition. Tensile properties results showed that the age hardening response of the alloys was decreased by dynamic precipitation and water quenching was an efficient method which is able to avoid this behavior in some extent.

Abstract: 440C martensitic stainless steels are widely used because of their good mechanical properties. The mechanical properties of 440C martensitic stainless steel were evaluated after heat treatment of these materials at various types of heat treatment processes. The initial part of this investigation focused on the microstructures of these 440C steels. Microstructure evaluations from the as-received to the as-tempered condition were described. In the as-received condition, the formations of ferrite matrix and carbide particles were observed in this steel. In contrast, the precipitation of M₇C₃ carbides and martensitic structures were present in this steel due to the rapid quenching process from the high temperature condition. After precipitation heat treatment, the Cr-rich M₂₃C₆ carbides were identified within the structures. Moreover, a 30 minutes heat-treated sample shows the highest value of hardness compared to the others holding time. Finally, the tempering process had been carried out to complete the whole heat treatment process in addition to construct the secondary hardening phenomenon. It is believed that this phenomenon influenced the value of hardness of the 440C steel.