Utilisation of silicon rubber to characterise tool surface quality during die compaction

Abstract

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.     

Effect of local volume fraction of microporosity on tensile properties in Al–Si–Mg cast alloy

Abstract

Porosity in Al–Si–Mg cast alloys utilised in automotive parts affects directly products quality, i.e. mechanical properties. In this study, the effect of micropores on mechanical properties has been investigated by X-ray tomography from the viewpoint of clustering micropores. The local volume fraction (LVF) of porosity was introduced to analyse the effect of clustering micropores. The statistical Weibull method was also used in order to explain strength of the alloy tested. The fracture strain decreased drastically from 17 to 3% on an inverse parabolic relationship with increasing porosity. In the case of the specimens that contain the largest pore higher than 100 m m, the ultimate tensile strength decreases monotonically. It is found that the fracture surface passes through high LVF regions. The fracture strain obviously depends on the ratio of LVF higher than 10%. It is confirmed that the LVF, which represents unevenly distribution of micropores cluster, is one of important dominant factor for managing the mechanical properties in the Al–Si–Mg cast alloy.     

Influence of atomising gas pressure on 63A solder powder in supersonic atomisation

Abstract

The atomising gas pressure is one of several important process parameters that affect the characteristics of the powder particles. The work analyses qualitatively the influence of the atomising gas pressure on 63A solder alloy fine powders. Also studied was the mechanism of the effect of the atomising pressure on the base of the air dynamics through the atomising 63A solder alloy experiment with different atomising pressures on the supersonic nozzle. The results indicate that 63A solder alloy fine powders may be attained, which can satisfy the SMT application requirement when the atomising gas pressure is at 0.7 MPa.     

Microstructural and textural evolution during large strain hot rolling (LSR) of Mg–Al (AZ31) alloy

Abstract

Grain refinement has been achieved through large strain rolling (LSR) in Mg AZ31 alloy. The evolution of microstructure and texture has been found to be dependent on the amount of reduction. After the critical amount of reduction, grain refinement proceeds through continuous dynamic recrystallisation (CDRX).     

Studies of microstructural changes upon retrogression and reaging (RRA) treatment to 8090 Al – Li – Cu – Mg – Zr alloy

Abstract

Microstructural changes upon retrogression, and retrogression and reaging (RRA) treatment to 8090 Al – Li – Cu – Mg – Zr alloy in the peak aged (T8) temper have been studied by XRD and TEM. The variation of hardness with retrogression, and retrogression and reaging (RRA) has been measured to assess RRA behaviour. XRD studies exhibited all the phases that would be expected in the system. Retrogression primarily caused dissolution of matrix strengthening δ' precipitates in the solution. Reaging the retrogressed state caused reprecipitation of the δ' precipitates in the matrix. Retrogression and reaging (RRA) treatments retained the strength of the conventional peak aged temper, but TEM observations revealed some microstructural changes, such as growth of δ', T₁ and S' phases, reduction of the dislocation densities, and generation of more dislocation loops and helices.     

Effects of homogenisation treatment on microstructure and hot ductility of aluminium alloy 6063

Abstract

Several homogenisation treatments were applied to direct chill (DC) cast ingots of aluminium alloy 6063, in order to analyse the resulting microstructures developed from these diverse conditions and their effects on the hot ductility of this alloy. Imaging was performed using scanning electron microscopy (SEM) and a focused ion beam (FIB) instrument. These techniques identified variations in distribution and morphology of second phase particles (AlFeSi and Mg₂Si). FIB results for the various AlFeSi particles correctly identify their shapes in three dimensions (3D). The particles were identified by energy dispersive spectroscopy (EDS) in the SEM, and by X-ray diffraction (XRD) for bulk samples. Hot tensile testing (HTT) was conducted between 470 and 600°C to asses the hot ductility for each condition. The inferior ductility of as cast samples was due to the poor bond strength of the β AlFeSi phase at the grain boundaries. Homogenised samples, which contain α AlFeSi, exhibited improved ductility. Samples that were water quenched following homogenisation were absent of Mg₂Si precipitates, when these elements remained in solid solution. These exhibited the highest ductility.     

Effect of Sr on primary α-Fe phase in liquid Al-11.5Si-0.4Mg cast alloy

Abstract

The effect of Sr on the sedimentation of primary α-Fe phase has been investigated at superheating temperatures of 760 and 900 °C. A convection free experimental technique was used to aid in quantifying the primary α-Fe particles sedimented at 600 °C for 4 h. Sr marginally decreases the formed particle weight at normal melting temperature (760 °C), but greatly increases the particle weight at the superheating temperature of 900 °C. Sr refines primary α-Fe particles at both temperatures, causing the increase of the number of primary α-Fe particles, especially when superheated at 900 °C. In addition, Sr causes a decrease in the particle volume fraction but an increase in the number of the sedimented particles, and a great increase in the depth of the sediment in the mould at higher superheating temperatures. These observations are interpreted in terms of the precipitation of Fe rich particles on suspended oxide films, and the rigidisation of suspended films at higher temperatures, possibly as a result of their change in chemistry, but especially as a result of inflation of their doubled-over form by hydrogen, and the effect this has on the multiplication of growing iron rich precipitates as a result of their mechanically unstable substrate.     

Method for welding highly crack susceptible magnesium alloy ZK60

Abstract

The highly crack susceptible magnesium alloy ZK60 plates of 2 mm thickness were successfully welded by laser beam welding (LBW) with filler strip, which has the advantages of low heat input and capability of adjusting the compositions of weld metal to a less susceptible level. The effects of the compositions of filler strips on the microstructures and mechanical properties of the joints were investigated. Compared with autogenous LBW, LBW with filler strip can produce a narrower joint and avoid the cracks and pits, which severely worsen mechanical properties of the joints. When the filler strip of ZK40 alloy is employed, the grains in fusion zone can be refined, and a high quality joint, with the ultimate tensile strength of 322 MPa up to 90·7% of the base metal, is obtained.     

Examination of HA230 turbine transition duct

Abstract

The present paper reports the results of an examination of a service run transition duct from one of Siemens' industrial gas turbines and the correlation between the findings for this, and those from the studies undertaken on laboratory exposed Haynes alloy 230 material. The studies have shown that there are changes in the microstructure and hardness of the material that can be related to temperature and time of exposure, and the information gained can lead to estimations of the average component operating temperature. Metallographic studies revealed a high level of heterogeneity of the grains in this transition duct.     

Solidification cracking in low alloy steel welds

Abstract

The high solidification cracking susceptibility of low C steel weld metals was investigated using pure Fe model alloys containing 0–0·23%C, 0–5%Ni and 0–0·0144%B. In addition, a few Fe–C–Ni ternary alloys were also tested. Solidification cracking susceptibility was tested using longitudinal varestraint and transvarestraint tests. Cracking was evaluated using crack length and brittleness temperature range criteria. The Fe–C alloys showed high cracking tendency in two regimes, the first in the ultralow carbon range of 0·03–0·05%C and the second in a narrow band close to 0·1%C. The cracking was much more than that attributable to solute segregation. In Fe–Ni and Fe–B alloys, cracking was a function of alloy content. Solidification cracking due to C and Ni was higher in the ferritic mode of solidification compared to the austenitic, unlike in stainless steels, where the ferritic mode provides high resistance to cracking. In Fe-C-Ni ternary alloys, cracking could be better related to composition in terms of a variable coefficient for C in the Ni equivalent. In the vicinity of 0·1%C, cracking was attributable to shrinkage due to solid state transformation from δ to γ in the brittle temperature range, and is similar to that occurring during continuous casting of steel. However, this factor did not appear to play a role in cracking in the ultralow C range of 0·03–0·05%C.