Medium Strength Aluminium Alloy Research Articles

Investigation of mechanical properties of metal matrix composites

Aluminium is one of the lightest engineering materials. It offers a greater strength to weight ratio. Due to the numerous ways in which aluminium's advantageous properties—including strength, lightness, corrosion resistance, recyclability, and formability—can be combined; it is employed in an increasing number of structural applications. Several researchers have been evaluated in order to combine some of the components of the mechanical and wear behaviour of stir cast aluminium metal matrix composites. Aluminium 6061 alloy, in which aluminium serves as the basic element, is selected as the matrix alloy in this project. Medium-strength aluminium alloy 6061 exhibits high corrosion resistance. The 6000 series alloy with the maximum strength is 6061, it is known as a structural alloy. Two alternate weight ratios of Al2O3, SiC, and aluminium matrix have been offered for the work, which is processed using a stir casting set-up. The samples are tested, and the results are reviewed. Density, hardness, and toughness increases but the tensile strength decreases with an increase in the reinforcement percentage.

Structure–Property Relationship in High-Strength Aluminum Alloys/Stainless Steel Brazed Joints

In many industrial sectors, for example, aerospace, automotive and high-performance electronic industries, there is a significant need to join dissimilar materials. In the case of medium-strength aluminum alloys, joints are commonly manufactured using Al-Si brazing fillers with a melting temperature of 575 °C. In comparison to medium-strength aluminum alloys, high-strength aluminum alloys exhibit lower melting temperatures. Therefore, the joining possibilities are limited. Due to the lower melting temperature of about 500 °C, Al-Ag-Cu brazing fillers allow the joining of these alloys. In this study, high-strength aluminum alloys/stainless steel joints were produced via induction brazing and vacuum furnace brazing. The mechanical properties of the joints were determined using tensile shear tests as well as fatigue tests at ambient temperature. The joints produced via induction brazing at 520 °C without holding time reached a maximum tensile shear strength of 32 MPa. The joints failed in the braze metal close to the reaction zone. The joints brazed in the vacuum furnace at 540 °C for 10 min reached a maximum tensile shear strength of 18 MPa. The fractures occurred in the reaction zone, especially inside the Al7Fe2Si intermetallic layer. The thickness of the intermetallic layers as well as the reaction zone had a significant influence on the joining strength and the fracture mechanism of the brazed joints. The results of the fatigue tests showed that the joints brazed without holding time achieved the defined limited number of cycles of 1 × 107 at a stress amplitude of 4 MPa. For all the fatigue-tested samples, the fracture occurred in the braze metal, especially in the eutectic. Hence, the reaction zone does not significantly influence the fracture mechanism of high-strength aluminum alloy/stainless steel brazed joints during cyclic loading.

Strength of Aluminum Alloys for Bridge Building

The resistance of aluminum alloys to the actions that are characteristic of operation in the load-bearing structures of bridge constructions, namely, fatigue, static, impact loads, and crack propagation, is studied. It is shown that, in bridge building, medium-strength aluminum alloys of the Al–Mg, Al–Mg–Si, and Al–Zn–Mg systems should be used. The specific features of deformation and fracture of aluminum alloys that affect their ductility, fracture energy, fracture toughness, and fatigue life are revealed.

Investigations of Multi-pass Friction Stir Welding for Al-Zn-Mg Alloy

Al-Zn-Mg alloy is a medium strength and non-weldable aluminium alloy. This alloy has high ballistic strength which makes it the primary choice material for military vehicles. Low energy solid state welding process such as friction stir welding (FSW) is the suitable welding technique for such non-weldable alloys. As the welded structure is the result of effects of thermal cycles and multi-stirring action experienced by parent material during welding, therefore, this study is carried out to investigate the thermal effect of multi-pass FSW process on mechanical properties and microstructure of Al-Zn-Mg alloy welded joint. Significant changes in the microstructure of nugget zone, thermo-mechanical affected zone (TMAZ) and heat affected zone (HAZ) were observed which further had affected the overall mechanical performance of the welded structure.

Aluminum foil reinforced by carbon nanotubes

In our research, the method of manufacturing an Al-carbon nanotube (CNT) composite by hot pressing and cold rolling was attempted. The addition of one percent of multi-walled carbon nanotubes synthesized by OCSiAl provides a significant increase in the ultimate tensile strength of aluminum. The tensile strength of the obtained composite material is at the tensile strength level of medium-strength aluminum alloys.

Influence of high temperature thermal treatment on grain stability and mechanical properties of medium strength aluminium alloy friction stir welds

A heat treatment of 2h at 535°C was applied to 6082T6 friction stir welds. One of the effects of post-welding heat treatment on microstructure was abnormal grain growth. The presence, in the same nugget, of zones with different grain size, is the key factor to understand why, after exposure at 535°C for 2h, abnormal grain growth is locally observed. The ductility substantially increased and tensile strengths remained comparable to those of as-friction stir welded samples. Particle evolution influenced microhardness values and determined deformation to fracture, even if abnormal grain growth appeared in the nuggets.

Precipitation hardening and hydrogen embrittlement of aluminum alloy AA7020

AA7020 Al–Mg–Zn, a medium strength aluminium alloy, is used in welded structures in military and aerospace applications. As it may be subjected to extremes of environmental exposures, including high pressure liquid hydrogen, it could suffer hydrogen embrittlement. Hydrogen susceptibility of alloy AA7020 was evaluated by slow strain-rate tensile testing, and delayed failure testing of hydrogen-charged specimens of air-cooled, duplexaged, and water-quenched duplex agedmaterials. The resistance to hydrogen embrittlement of the alloy was found to be in the order of air-cooled duplex aged alloy > as-received (T6 condition) > water quenched duplex aged material.

Hydrogen embrittlement properties of medium-strength 7000 series aluminum alloys in high-humidity air

For medium-strength aluminum alloys 7003 and 7N01 having average (symbolized with S) or upper limit (symbolized with H) in the contents specified in JIS, SSRT tests were carried out in humid air with 90% relative humidity by using a smooth tensile specimen machined from the alloy plates with temper T5, T6 or T7. The susceptibility to hydrogen embrittlement (HE) was evaluated and the relation between the crack extension and microstructural factors was discussed. The following four materials were found to satisfy the useful combination in properties between a low HE susceptibility and yield strength σYS≧320 [MPa]; 7003H-T5, 7N01S-T5, -T6 and -T7. It is supported from microstructural observations that the relatively high HE susceptibility in 7003S-T6 or 7N01H-T6 results from a heterogeneous distribution or a smaller size in grain boundary precipitates to favor intergranular cracking (IGC) , while the low susceptibility in 7003S-T7 or 7N01S-T6 is attributed to the grain boundary hydrogen accumulation reduced by trapping effects of matrix precipitates, dispersoids or second phase inclusions, leading to retardation of IGC extension.

Analysis of Metal Flow through a Porthole Die to Produce a Rectangular Hollow Profile with Longitudinal Weld Seams

A detailed analysis of metal flow through a porthole die to produce a rectangular hollow aluminium profile was performed by means of three-dimensional FE simulation using DEFORM 3D. It was aimed at revealing the flow patterns of a medium-strength aluminium alloy 7020 through a porthole die and gaining an insight into the formation of longitudinal weld seams inside the welding chamber during extrusion. In the case of extruding a rectangular hollow profile through a porthole die with four ports, two neighbouring ports were different from each other. Using an FE model including these two ports, different flow patterns of two individual metal streams were revealed. The 3D FE simulation also showed how two unequal metal streams contacted each other and became bonded in the welding chamber under a certain hydrostatic pressure and at a certain temperature, before the metal flew through the die bearing. The difference in velocity between the metal streams led to uneven flow at the die bearing and thus a wavy extrusion nose.

Influences of pulsed current tungsten inert gas welding parameters on the tensile properties of AA 6061 aluminium alloy

Medium strength aluminium alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. In any structural application of this alloy consideration its weldability is of utmost importance as welding is largely used for joining of structural components. The preferred welding process of aluminium alloy is frequently tungsten inert gas (TIG) welding due to its comparatively easier applicability and better economy. In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. Many considerations come into the picture and one need to carefully balance various pulse current parameters to arrive at an optimum combination. Hence, in this investigation an attempt has been made to study the influence of pulsed current TIG welding parameters on tensile properties of AA 6061 aluminium alloy weldments.

Effect of water vapour pressure and frequency on fatigue behaviour in 7017-T651 aluminium alloy plate

The effect of water vapour pressure on fatigue crack growth in a commercial medium strength aluminium alloy is analysed in this investigation, with particular emphasis on its relation to environmental exposure. Crack growth velocities were measured in high-purity water vapour environments with pressures ranging from 10 −5 Pa to 1300 Pa and testing frequencies between 1 Hz and 10 Hz. A detailed microscopic survey of the fracture surfaces was also performed. Different types of striations were found and correlated with water vapour exposures. Experimental results agree quite well with a hydrogen embrittlement model based on the proposals by R. P. Wei and co-workers.

Improved overhead line conductors using aluminium alloy 1120

Power conductors utilising the new high conductivity medium strength aluminium alloy type 1120 have been used for transmission and distribution lines in Australia since 1984. Unlike traditional aluminium alloys such as 6201 and 5005 the 50% increase in strength of alloy 1120 over standard EC grade aluminium is accompanied by only a slight reduction in conductivity. Overhead line conductors using this alloy provide lower I/sup 2/R losses without appreciable capital cost penalty. Introduction of these new alloy conductors provides a significant development in transmission line technology. This paper traces the introduction of this alloy in Australia, the development and testing of such conductors, together with details of its application by one major utility. >

Effect of grain size on the crack resistance of aluminum alloys

Crack resistance is an important characteristic of the structural strength of materials. The reliability criteria for articles depend upon it, i.e., ‘safe damage’ and ‘safe life.’ The first criterion is governed by the capacity of a material to provide article operation in the presence of cracks, and the second is governed by the time to generation of the first crack. Thus in order to evaluate crack resistance it is necessary to determine material resistance to crack generation and development. In this work resistance to crack generation and development is evaluated for wrought medium-strength aluminum alloys AMg6, AK4-1, and high-strength alloy V96ts which has a matrix (pseudo-single-phase) structure.

Creep of medium and high strength aluminum alloys at normal temperature in moist atmospheres

Direct data have been obtained for the creep of high- and medium-strength aluminum alloys in the stress range of O.6–1.2 of the nominal yield strength σ0.2 in laboratory air and in aqueous NaCl solution at room temperature. On this basis using known theories approximating functions have been determined for the creep curves. Stress σ0.2 serves as a natural boundary for the macroelastic and macroplastic regions in the first of which creep is only transient, and in the second there are transient, quasisteady-state, and accelerated stages. Extrapolated estimates of creep strain in the macroelastic region from data measured in the macroplastic region are not physically competent. However, a tendency towards an increase in ductility with an increase in time to failure at stresses greater than σo.2 makes it possible to estimate by extrapolation the time for onset of the accelerated creep stage with low test stresses from measured values at greater stresses in the macroplastic region. Fractographic and strain indices revealed the harmful effect of moist atmospheres on the deformation and failure resistance of alloys with prolonged loading.

中強度アルミニウム合金のじん性の評価方法

A testing method has been investigated to evaluate quantitatively the toughness of medium-strength aluminum alloys using sheet-type specimens. In this method, toughness was evaluated by the balance of the following two values; the resistance to crack initiation and the resistance to crack propagation, which were obtained by the static tear test at room temperature.It was considered that notch strength was an index of the resistance to crack initiation. In this method, notch strength was defined by the maximum load in the load-deflection curve of the tear test. For the resistance to crack propagation, the slope of the load-deflection curve during crack propagation was considered as its index.In the load-deflection curve, the toughness values are expressed as follows:1) as an index of the resistance to crack initiationNotch strength: σmax=Pmax/A(kg/mm2)Pmax: the maximum load of a load-deflection curve (kg)A: net sectional area (sectional area at the notch) (mm2)2) as an index of the resistance to crack propagationUnit slope=U. S.=Actual slope/A(kg/mm/mm2)Actual slope is the slope of the load-actual deflection curve during crack propagation. (kg/mm)It was recognized that there existed correlations between σ0.2 and (σmax)2 and between (σmax)2 and the U. S. value for about twenty commercial aluminum alloys with no defects. The relation between (σMax)2 and σ0.2, which was considered to show the resistance to crack initiation, was linear in the whole range. The relation between (σmax)2 and the U. S. value, which showed the resistance to crack propagation, was linear only in some regions.