A calorimetric analysis of the response to heating of EN AW-2014 alloy formed in the liquid, solid and semi-solid states

A calorimetric analysis was undertaken to understand the phase evolution during DC cast, extruded and thixo-forming of EN AW-2014 alloys. Extruded EN AW-2014 alloy responds to a heating cycle by the precipitation of the equilibrium theta-CuAl2 phase and its nonequilibrium precursors. This precipitation sequence is largely missing in the cast and thixoformed EN AW-2014 counterparts, suggesting that the precipitation capacity of these alloys is largely exhausted at very low temperatures. An additional endotherm is noted in the cast and thixoformed counterparts evidencing an additional soluble constituent, Cu2Mg8Si6Al5. Extruded EN AW-2014 alloy undergoes recrystallization between 500 degrees C and 550 degrees C while cast and thixoformed alloys undergo only grain growth. Cooling from solid-state forming is relatively faster and helps to retain much of Cu in solution offering a full precipitation sequence during a subsequent heating cycle ensuring substantial age hardening in the extruded alloy. A separate solution treatment is required to take advantage of the age hardening capacity of cast and thixoformed alloys

Synthesis of Al-SrB6 composite via powder metallurgy processing

The potential of powder metallurgy processing for the manufacture of Al-SrB6 composites was explored. Al4Sr particles fractured extensively during the ball milling of Al-15Sr/Al-4B powder mixtures. There was no interaction between the Al4Sr and AlB2 compounds across the section of the aluminium grains in the as-milled state. SrB6 formed, when the ball milled powder blends were subsequently annealed at sufficiently high temperatures. Ball milling for 1 h was sufficient for SrB6 to become the major constituent in powder blends annealed at 700 degrees C while it took 2 h of ball milling for powder blends annealed at 600 degrees C. Higher annealing temperatures and longer ball milling time encouraged the formation of the SrB6 compound while the latter made a great impact on the microstructural features of the Al-SrB6 composite. The SrB6 compound particles were much smaller and more uniformly distributed across the aluminium matrix grains in powder grains ball milled for 2 h before the annealing treatments at 600 degrees C and 700 degrees C

Low-temperature synthesis of MgB2 via powder metallurgy processing

Ball-milled Mg/B2O3 powder blends reveal interpenetrating layers of deformed magnesium and boron oxide grains that are increasingly refined with increasing milling time. Boron oxide is reduced by Mg and MgO thus formed reacts with the remaining B2O3 to produce Mg-3(BO3)(2) during ball milling for 30 min. Both B2O3 and Mg-3(BO3)(2) react with Mg to produce MgB2 upon further ball milling. An annealing treatment can be employed when ball milling is performed for less than 1 h as thermal exposure of the ball-milled Mg/B2O3 powder blends also leads to the formation of MgB2. The above reactions take place between 500 and 700 degrees C when the Mg/B2O3 powder blend is ball milled for 30 min, and between 450 and 550 degrees C, after ball milling for 1 h. This is a very attractive route owing to processing temperatures where the volatility of Mg is no longer a problem

Effect of Cr and Zr on the grain structure of extruded EN AW 6082 alloy

The effects of Cr and Zr addition on the coarse grain surface layer in EN AW 6082 tube extrusions were investigated. The decoration of the tube surfaces and the weld seams with coarse recrystallized grains reflects the strain as well as the temperature gradients that predominate across the section of the tubes during extrusion. The recrystallization resistance provided by Mn does not suffice to avoid the coarse surface grains. With structural features that are almost identical to those of the base 6082 alloy, the 6082 alloy with 0.06 wt% Zr also fails to offer any improvement. The coarse grain surface layer is much thinner and recrystallization is entirely avoided across the weld seams upon the addition of 0.15 wt% Cr. The superior recrystallization resistance of the revised alloy is attributed to the increase in the population of the Cr-rich Al(Cr,Mn,Fe)Si as well as (Al, Si)(3)Zr dispersoid particles. It is reasonable to conclude that the coaddition of Zr and Cr has a favourable impact on the resistance to recrystallization of EN AW 6082 alloy

Melt treatment of Al-Si foundry alloys with B and Sr additions

Individual Sr and B additions to Al-Si alloy melts fail to provide either grain refinement or modification. Sr and B must be used together to achieve both features for high-quality sound castings. Sr and B solutes in addition to insoluble SrB6 particles are introduced to the melt when Sr and B are used together. SrB6 particles and B solutes, which form the AlB2 particles later during solidification, are believed to be responsible for the marked improvement in grain refinement in the co-addition practice. Sr atoms in liquid solution, on the other hand, are adsorbed on the surface of the Si plates leading to twinning once the melt cools to the eutectic solidification temperature. A series of experiments have shown that a very fine grained matrix and a fine fibrous eutectic are readily obtained when the AlSi7Mg0.3 alloy is inoculated with 100 ppm B and 150 ppm Sr

A calorimetric analysis of the precipitation reactions in AlSi1MgMn alloy with Cu additions

The DSC spectrum of the AlSi1MgMn alloy with 0.05 wt% Cu confirms the well established precipitation sequence for ternary Al-Mg-Si alloys: supersaturated solid solution -> GP zones -> beta" -> beta' -> beta. The precipitation activities are displaced to lower temperatures with increasing Cu concentration. Additional Cu -bearing metastable precipitates, L, Q and theta, are evidenced by the change in the peak configuration in the DSC spectra of Cu -added AlSilMgMn alloys. The following precipitation sequences; SSSS -> GP -> theta' -> L -> beta" -> Q' -> beta' -> beta/Q/theta and SSS -> GP -> theta" ->theta' -> L -> beta" -> beta'-> beta/theta offer a plausible account of the revised peak configurations in the DSC spectra of the AlSiMgMn alloy with 0.15 wt% Cu and with at least 0.3 wt% Cu, respectively. (C) 2017 Elsevier B.V. All rights reserved

Processing of twin-roll cast thin AlFeSi strips for the manufacture of aluminium finstock

The thin strips produced with the new generation twin roll casters experience profoundly different temperature and strain gradients in the caster roll gap and thus require different down stream processing cycles. An attempt was made in the present work to identify processing cycles for the manufacture of finstock from thin AlFeSi strips. The grain structure in strips homogenized directly at the cast gauge is reorganized through growth processes while the grain structure in strips homogenized after cold rolling is reorganized via recrystallization. Finstock samples cold rolled without a homogenization treatment start to recrystallize at 300 degrees C in a very sluggish fashion whereas finstock samples submitted to a homogenization treatment undergo a faster recrystallization starting at 225 degrees C. Finstock with intermediate temper mechanical properties can be more easily achieved with a back-annealing process cycle without a homogenization treatment owing to a sluggish recrystallization. Soft temper finstock, on the other hand, requires a process cycle with a homogenization treatment

Optimising the T6 heat treatment for gravity cast AlSi7MgCu0.5 alloy V8 cylinder heads

Alternatives to the Standard T6 heat treatment that relied on a 5-h solution heat treatment at 490 degrees C were investigated in effort to reduce the heat treatment cycle time for the manufacture of AlSi7MgCu0.5 alloy V8 cylinder heads without sacrificing the mechanical properties while providing extra capacity in the heat treatment plant. The optimum T6 heat treatment process was identified to be a SHT at 545 degrees C for 1 h followed by ageing treatment at 180 degrees C for 3 h. Mechanical properties of the cylinder heads thus manufactured were markedly superior while the total heat treatment duration was reduced by 2.5 h with respect to the Standard heat treatment. This implied a capacity increase of %61 and rendered the undertaking of a major customer order possible

Effect of Welding Parameters on the Microstructure and Strength of Friction Stir Weld Joints in Twin Roll Cast EN AW Al-Mn1Cu Plates

Twin roll cast EN AW Al-Mn1Cu plates were butt welded with the friction stir welding process which employed a non-consumable tool, tilted by 1.5A degrees and 3A degrees with respect to the plate normal, rotated in a clockwise direction at 400 and 800 rpm, while traversing at a fixed rate of 80 mm/min along the weld line. Microstructural observations and microhardness tests were performed on sections perpendicular to the tool traverse direction. Tensile tests were carried out at room temperature on samples cut perpendicular to the weld line. The ultimate tensile strength of the welded EN AW Al-Mn1Cu plates improved with increasing tool rotation speed and decreasing tool tilt angle. This marked improvement in ultimate tensile strength is attributed to the increase in the heat input owing to an increased frictional heat generation. There appears to be a perfect correlation between the ultimate tensile strength and the size of the weld zone. The fracture surfaces of the base plate and the welded plates are distinctly different. The former is dominated by dimples typical of ductile fractures. A vast majority of the intermetallic particles inside the weld zones are too small to generate dimples during a tensile test. The fracture surface of the welded plates is thus characterized by occasional dimples that are elongated in the same direction suggesting a tensile tearing mechanism

Cooling slope casting to produce EN AW 6082 forging stock for manufacture of suspension components

The potential of cooling slope casting process to produce EN AW 6082 forging stock for the manufacture of EN AW 6082 suspension components was investigated. EN AW 6082 billets cast over a cooling plate offer a fine uniform structure that can be forged even without a separate homogenization treatment. This is made it possible by the limited superheat of the melt at the start of casting and the fractional solidification that occurs already on the cooling plate. Suspension parts forged from cast and homogenized billets with or without Cr all showed a uniform structure, and the hardness reached HV 110 after the standard artificial ageing treatment