Abstract: Al-Zn-Mg alloys are widely used construct material for wide range of application including automotive industry, building, and aviation. Scandium is rare earth metal, which modifies structure of semi-products and can lead to increasing of tensile and yield strength because of Al3Sc intermetallics of nanoscale size. This paper describes results of influence of small addition of scandium (0,08 wt. %) on mechanical and corrosion properties of cold-rolled sheets of 1913 alloy. 1913 is Russian medium strength corrosion resistant weldable Al-Zn-Mg alloy with addition of Cu for improvement of stress corrosion resistance and Mn with Zr for structure improvement. It is shown that addition of Sc transforms kinetics of artificial aging and accelerates decomposition of solid solution, besides tensile strength increases up to 50 MPa in artificially aged tempers. Changes in microstructure and quench sensitivity are described; results of intergranural corrosion, exfoliation and stress corrosion tests are introduced after different heat treatment including peak strength aging and overaging tempers.
Abstract: Colour of the anodised Al-Mg-Si alloys was quantified by spectrophotometric method defining L* (lightness), a* (greenness-redness) and b* (blueness- yellowness) values. All alloys exhibited yellow and green colour. The yellowness of the anodised surfaces increased significantly with the increase of Cu while increasing Mn reduced the greenness. Effect of trace elements V and Ni was negligible while Zn caused slightly yellowness. Fe reduced the lightness of the surfaces, while its effect on colour was insignificant. Smut layer being formed during alkaline etching (prior to anodising) was desmutted/deoxidised in different acid solutions, some of which failed to clean the etched surfaces. Remaining smut however caused minor effect on colour.
Abstract: In order to improve the intergranular corrosion resistance of high strength Al-Mg alloys, the effect of stabilizing treatment was systematically investigated. Microstructure evolutions of Al-Mg alloys after different stabilizing treatments have been studied by scanning electron microscopy and optical microscopy. Mechanical properties and corrosion resistance were measured. It was found that the mass loss of samples after sensitizing treatment decreased with an increase in the stabilizing temperature. It was suggested that the susceptibility to intergranular corrosion for high strength Al-Mg alloys has a strong relation to the stabilizing temperature that modify the morphology and distribution of precipitates. The precipitates continuously precipitated along the grain boundary when the stabilizing temperature was lower than 250°C, corresponding to a poor corrosion resistance. However, the precipitates randomly precipitated in the matrix as globular particles, and discontinuously precipitated at the grain boundary after stabilized at 250°C and 275°C, resulted in an improved intergranular corrosion resistance.
Abstract: Creep behavior of an Al-0.3%Mg-0.5%Si alloy affected by pre-aging condition was investigated to obtain fundamental knowledge on the thermal stability in the service temperature range for the precipitation-hardened aluminum heat-exchanger. The alloy was aged at 175 °C for 3 h (under-aged) and 24 h (peak-aged), after solution treatment, and then subjected to creep testing at temperatures of 150 °C and 200 °C. When the creep temperature was 150 °C, the under-aged (UA) specimen showed a lower creep rate than that of the peak-aged (PA) specimen. On the other hand, when the creep temperature was 200°C, both specimens showed almost the same creep rate. In other words, the UA specimen had higher creep resistance than the PA specimen at 150 °C, whereas this advantage disappeared at 200 °C. The difference was thought to originate from the precipitation during creep testing.
Abstract: The automotive applications using heat-treatable aluminum cast alloys are designed for high impact energy which can be improved using specified casting process and different heat treatment. In this study an economical and convent squeeze casting machine was used to produce the u-profile with 3mm wall thickness under controlled solidification conditions. The casted samples were used for mechanical and metallographical characterization. The mechanical properties of alloys containing different amount of Fe, Mn und Mg were determined as a function of different heat treatment condition such as modified T7 and Silicon Spheroidization Treatment (SST). The microstructure of casted alloys were quantificational determined by a combination of light optical microscope and scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) module to identify the morphology and chemical composition of intermetallic eutectic phases. The results of Charpy impact test show that impact energy increases after modified T7 or SST heat treatment significantly compared with the as cast state. Furthermore the impact energy is less in the higher Mg containing alloys (0.15wt.%) compared with the less Mg containing alloy (0.07wt.%).
Abstract: A6N01 (6005C in ISO) base metal is applied for cantilever type fatigue test over 108 cyclic number. Fatigue strength decreases over 107
and after testing, new prediction formula of fatigue life at high cycle regeion which named YENs formula is proposed for light metal and their welded joints. This formula is shown as below.
Log (σa/σp) =k Log (Nf-N0)+m
σa is stress amplitude, σp is proof stress k is depend on stress concentration factor
Nf is fatigue life without residual stress and No is discrepancy due to residual stress.
m is material constant. This formula is a hypothesis and it is required to accumulate much more fatigue data for many kind of alloys and their welded joints.
Abstract: Effect of thermomechanical processing on creep resistance at 150°C of an Al-5.6Cu-0.72Mg-0.5Ag-0.32Mn-0.17Sc-0.12Zr (wt. %) alloy was examined. It was shown that increasing strain prior to artificial aging provides achieving high strength. However, a degradation of the creep resistance, i.e., significant decrease in the rupture time and increase in the minimal creep rate, took place, concurrently. The effect of cold rolling on the strength and creep resistance is discussed in relation with the strain effect on the dispersion of secondary phases. The increase in strength and degradation of creep properties of the alloy subjected to cold working before ageing result from superposition of two competitive processes. First, an increase in the lattice dislocation density facilitates the precipitation of Ω-phase plates with high aspect ratio, leading to increase in the static strength at room temperature. Second, acceleration of the diffusion processes results in coarsening of strengthening phase in grain/subgrain interiors and precipitation of Ω-phase on deformation-induced boundaries during creep that deteriorates creep resistance.
Abstract: Tensile tests on smooth and notched axisymmetric specimens were carried out to determine the large strain work-hardening curves and the ductile fracture characteristics of an AA6060 aluminium alloy for three different processing routes. The alloy was processed in three subsequent steps: 1) casting and homogenization, 2) extrusion, and 3) cold rolling and heat treatment to obtain a recrystallized grain structure. After each processing step, the material was tested after natural ageing for more than one week. A laser-based extensometer was used to continuously measure the average true strains to failure in the minimum cross-section of the specimens and the true stress-strain curves were calculated. Since these curves are influenced by necking, they do not represent the correct work-hardening of the material. Accordingly, finite element (FE) simulations of the tensile tests on the smooth axisymmetric specimens were conducted to determine the work-hardening curves to failure, using an optimization tool that interfaced with the nonlinear FE code and the experimental stress-strain curves as objectives. The microstructure of the alloy was characterized after the three processing steps by optical and scanning electron microscopy, and fractography was used to investigate the failure mechanisms.
Abstract: In this study, the effect of electroless Ni-P plating on the fatigue strength of dilute Al-Si alloys was investigated. As results, the following points were clarified. Fatigue strength of the specimen subjected to zincate treatment only after furnace cooling treatment was almost the same as the furnace cooling only. Fatigue strength of the specimen subjected to Ni-P plating after furnace cooling treatment, was reduced overall, except for high-stress region, rather than one of non-processing materials. Fatigue strength of the specimen subjected to Ni-P plating after aging treatment showed a clear increase in comparison with one of non-processing materials. Breaking elongation of the specimen subjected to Ni-P plating after aging treatment showed no significant changes in comparison with one of non-processing materials. On the other hand, breaking elongation of the specimen subjected to Ni-P plating after furnace cooling treatment reduced by half in comparison with one of non-processing materials. Especially, it seems that poor fatigue strength and ductility of plating materials are mainly caused due to interaction between surface precipitates and hydrogen gas.
Abstract: The mechanisms of fatigue crack initiation due to second phase particles are studied in 2050-T8 and 7050-T74 plate material. The particles in the specimens gauge lengths are imaged using SEM at the initial state. In 7050-T74, Mg2Si particles are very often cracked before any loading, whereas Al7Cu2Fe particles are not. In 2050-T8, the fraction of (Al, Cu, Fe, Mn) particles initially cracked is larger than that of Al7Cu2Fe in 7050-alloy, but lower than that of Mg2Si particles for similar sizes. For (Al, Cu, Fe, Mn) particles, the proportion of cracked particles increases when the modified shape ratio (aspect ratio including orientation versus rolling direction) increases. This effect is present but less pronounced for Mg2Si particles in 7050-T74. Fatigue cracks initiate at cracked (Al, Cu, Fe, Mn) particles in 2050-T8 alloy, and at both Al7Cu2Fe (cracked during cycling) and Mg2Si in 7050-T74 alloy.