Corrosion behaviour of powder metallurgical and cast Al-Zn-Mg base alloys

The behaviour of Al-Zn-Mg base alloys produced by powder metallurgy and casting has been studied using potentiodynamic polarisation in 0.3% and 3% NaCl solutions. The influence of alloy production route on microstructure has been examined by scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectrometry. An improvement in performance of powder metallurgy (PM) materials, compared with the cast alloy, was evident in solutions of low chloride concentration; less striking differences were revealed in high chloride concentration. Both powder metallurgy and cast alloys show two main types of precipitates, which were identified as Zn-Mg and Zr-Sc base intermetallic phases. The microstructure of the PM alloys is refined compared with the cast material, which assists understanding of the corrosion performance. The corrosion process commences with dissolution of the Zn-Mg base phases, with the relatively coarse phases present in the cast alloy showing ready development of corrosion.     

Simulating the yield strength of cast alloys in the Al-Mg system

A physical model has been developed for determining the yield strength of alloys in the Al-Mg system in the cast state. The model takes into account the heterogeneity of distribution of the alloying element caused by dendrite liquation, as well as distribution specifics of eutectic inclusions. It is demonstrated that peripheral layers of dendrite cells enriched in the alloying element do not make a significant contribution to the yield strength of a cast alloy.     

Advances in optimisation of mechanical properties in cast TiAl alloys

The room temperature tensile properties of a number of cast TiAl-based alloys, which have been grain-refined either by additions of boron or by a new quenching and ageing treatment, have been assessed. It has been found that in the alloys which have been grain-refined by boron addition, the size of the titanium boride particles, which is strongly influenced by the size of the cast samples, is an important factor in limiting the tensile ductility. The tensile properties of samples which have been quenched and aged can be significantly improved and it has been shown that this grain refinement technique, which is based on the massive transformation, can be applied to a wide range of alloys. Quenching to above the ductile-to-brittle temperature, but below the temperature at which the massive transformation occurs, reduces the tendency for cracking during this type of heat treatment. The potential for producing cast components using these two approaches to grain-refinement is discussed.     

Evaluation of the effects of variations in chemical composition on the quality of Al-Si-Mg,Al-Cu,and Al-Zn-Mg cast aluminum alloys

The effect of slight variations in chemical composition on the quality of cast aluminum alloys from three different major alloy systems was evaluated. For the evaluation of the alloy quality, an index Q _D adjusted to damage tolerance requirements that are currently involved for the design of advanced lightweight structures is used. The quality index Q _D accounts for tensile strength and ductility as well as for material failure through yielding or fracture. For this investigation, experimental results obtained for variations in chemical composition of the alloy systems Al-Si-Mg, Al-Cu, and Al-Zn-Mg were exploited. In total, castings from 37 different batches from 10 aluminum alloys, varying in chemical composition, were evaluated. Quality characterization and alloy quality ranking were made by evaluating results of 512 tensile tests using the index Q _D as well as, for comparison, the quality index Q, which is currently used by the industry. The results obtained involving the index Q _D seem to be more realistic, from the viewpoint of damage tolerance design requirements.     

Influence of titanium additions on the properties of Al−Zn−Mg system cast alloys

Conclusion Addition of titanium increases the strength and plasticity of Al–Zn–Mg system casting alloys. The alloys with 0.2–0.3% Ti have the best mechanical properties. These alloys strengthen during natural and artificial aging without preliminary hardening. The highest strength is reached after hardening and artificial aging. Fracture of the alloys after heat treatment has a ductile character. Local deformation occurs nonuniformly in the alloys. The alloys are not prone toward general or intergranular corrosion.All-Union Scientific-Research Institute for Electrical Machinery. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 48–50, February, 1990.     

Effect of high-temperature pre-precipitation on mechanical properties and stress corrosion cracking of Al-Zn-Mg alloys

1　INTRODUCTIONMediumandhighstrengthAl Zn Mgseriesaluminumalloysarethe primaryweldingstructurematerialsofaerocrafts ,transportationvehiclesandmilitaryequipments[1,2 ] ,duetoitsbetterweldabilityandexcellenttechnologicalproperty .Buttheexten siveutilizationofthesealloysishamperedbyitspoorstresscorrosioncracking (SCC)resistance[3,4 ] .Ac cordingly ,manystudieshavebeenconcernedwithsuchaproblemashowtoimprovestresscorrosionre sistanceofAl Zn Mgalloyswithnon deterioratedstrength[3,58] .Atpres…     

Solidification path calculations of Al-Zn-Mg alloys in Al-rich corner

The solidification paths of Al-Zn-Mg alloys in the Al-rich corner were investigated. The thermodynamic data for the calculation are obtained by direct coupling with the CALPHAD software Thermo-Calc via its TQ6-interface and the COST2 database. The influences of the initial compositions and the extent of solid back diffusion on the solidification path were numerically investigated by sample calculation of the ternary Al-Zn-Mg alloys. The calculation results of solidification paths of the selected alloys: Al-Zn-3 Mg(in wt.%), Al-5 Zn-10 Mg, Al-2.5Zn-15Mg, Al-10Zn-20.5 Mg, Al-8Zn-25 Mg, were: L→(L+α-Al), L→(L+α-Al)→(L+α-Al+TAU), L→(L+α-Al)→(L+α-Al+Al Mg_β), L→(L+α-Al)→(L+α-Al+TAU)→(L+α-Al+TAU+Al Mg_β), L→(L+α-Al)→(L+α-Al+Al Mg_β)→(L+α-Al+TAU+Al Mg_β), respectively. The results show that the initial compositions and the extent of solid back diffusion have a great influence on solidification path, and the amounts of eutectic phase increase with the decrease of the solid back diffusion coefficient. The equilibrium solute partition coefficients for Zn and Mg in alloys are also calculated and their influence on micro-segregation in the primary solidification of Al-5Zn-10 Mg alloy is analyzed.     

Microstructure and mechanical properties of lost foam cast 356 alloys

Microstructure and mechanical properties of lost foam cast aluminum alloys have been investigated in both primary A356(0.13% Fe) and secondary 356(0.47%). As expected, secondary 356 shows much higher content of Fe-rich intermetallic phases, and in particular the porosity in comparison with primary A356. The average area percent and size(length) of Fe-rich intermetallics change from about 0.5% and 6 μm in A356 to 2% and 25 μm in 356 alloy. The average area percent and maximum size of porosity also increase from about 0.4% and 420 μm to 1.4% and 600 μm, respectively. As a result, tensile ductility decreases about 60% and ultimate tensile strength declines about 8%. Lower fatigue strength was also experienced in the secondary 356 alloy. Low cycle fatigue(LCF) strength decreased from 187 MPa in A356 to 159 MPa in 356 and high cycle fatigue(HCF) strength also declined slightly from 68 MPa to 64 MPa.     

Effect of minor Sc and Zr on microstructures and mechanical properties of Al-Zn-Mg based alloys

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