Horng-Yu Wu

Solid-state bonding of iron-based alloys, steel–brass, and aluminum alloys

Abstract Many genuine solid-state-bonding experiments have been performed using a wide range of metals; the latter includes superplastic ultra-high-carbon steel, Fe–Ni–Si alloy, manganese steel, brass, stainless steel, iron-silicon alloy as well as superplastic aluminum alloys 5083 and 7475. The roll-bonding process was employed to study the ability to mechanically bond (one kind of solid-state bond) iron-based alloys at intermediate temperatures. Press bonding was meant to determine the effect of three interconnecting factors—temperature, time, and deformation—on the strength of the diffusion bond. The results and analysis conclude that diffusion bonding is difficult to achieve without successful mechanical bonding preceding it.

Deformation characteristics of fine grained magnesium alloy AZ31B thin sheet during rapid gas blow forming

Abstract Decreasing the forming time in gas blow forming using fine grained Mg alloy AZ31B thin sheet with a thickness of 0·6 mm was studied in this work. Tensile tests and gas blow forming using stepwise pressurisation profiles were performed to explore the deformation behaviour of a fine grained AZ31B Mg alloy sheet. The alloy sheets were successfully deformed into hemispherical domes using two proposed stepwise pressurisation profiles during gas blow forming. As a result, significant reduction in forming time was achieved. Maximum effective deformation rates of 1·02 × 10–2 and 1·98 × 10–2 s–1 were obtained at 300 and 370°C respectively. It was feasible to form a hemispherical dome with a height of 20 mm in less than 80 s at 370°C. The results confirmed that the thickness distribution along the centreline of the formed dome was sensitive to the pressurisation profiles. A higher thinning effect was observed at 370°C due to the higher deformation rate imposed during forming. Grain growth was not a serious problem for forming even at 370°C, and static grain growth should be the major factor resulting in grain growth during forming.

Deformation behaviour and formability of LZ90 Mg alloy

Abstract This work examined the deformation characteristics of a LZ90 Mg alloy sheet with a thickness of 0˙6 mm using uniaxial tension and press forming tests at various temperatures. The influences of anisotropy and temperature on deformation behaviour were investigated. Formability parameters such as average plastic strain ratio, planar anisotropy and work hardening exponent were determined by tensile test results. The forming limit diagrams have been experimentally evaluated at various temperatures. Anisotropic behaviours were observed in the mechanical properties at all test temperatures. The tensile properties and formability parameters were correlated with the forming limit diagrams.

Effect of inverted pressurisation profile on deformation characteristics of 5083 aluminium alloy during superplastic forming

Abstract Decreasing the cycle time for superplastic forming of a commercially available superplastic 5083 aluminium alloy has been studied in the present work by use of an inverted pressurisation profile. A right cylindrical cup with a depth/ diameter ratio of 0·5 could be superplastically gas pressure formed in less than 100 s. The deformation behaviour was similar to that of constant strain forming during the free bulging stage. In this stage, a stress state gradient from the pole to the edge of the formed dome was observed. Plasticity controlled growth of cavities was thought to be the mechanism for the increase of cavity volume fraction during forming. After the centre point of the deformed sheet touched the die surface, the metal flow pattern was found to be different from that of the traditional approach. The minimum thickness was not located at around the bottom corner of the cylindrical cup rather it was located ~ 7.5 mm away from the bottom centre of the cup with radius 20 mm. Significant cavity nucleation and coalescence caused higher cavity growth rates at large strains, owing to the continuous increase in strain rate resulting from the imposed pressurisation profile.

Rate and Orientation Dependence of Formability in Fine-Grained AZ31B-O Mg Alloy Thin Sheet

Uniaxial tension and press forming tests were carried out at two different strain rates and temperatures to investigate the formability of fine-grained AZ31B-O Mg alloy thin sheet. Formability parameters were determined by tensile test results. The tensile properties and formability parameters were correlated with the forming limit diagrams. The present work focused on the effects of loading orientation and deformation rate on formability. Anisotropic behaviors were observed in the mechanical properties. Maximum strengths were obtained in the direction perpendicular to the rolling direction (RD). It can be concluded that the formability of the rolled fine-grained AZ31B-O Mg alloy sheet can be influenced by loading orientation and deformation rate. Stretch formability can be enhanced at a higher deformation rate, resulting from a lower anisotropy and a higher work hardening effect. In contrast, the drawing processes can be performed at a lower deformation rate to take advantage of a higher anisotropic behavior. Specimens with the RD parallel to the major strain in the press forming tests can enhance stretch formability, whereas specimens with the RD perpendicular to the major strain can improve deep-drawability.

Deformation behaviour in superplastic 5083 Al alloy during biaxial gas pressure forming with lubrication

Abstract Effect of lubrication on deformation behaviour of a superplastic material has been given little attention, although it is important for industrial application. In this paper, a superplastic 5083 Al alloy under biaxial deformation was investigated by deforming the sheet into a cylindrical die cavity with and without lubrication. Several interrupted tests were performed to bulge the sheets to various depths for two different strain rates, the formed parts were then utilised to evaluate the effect of lubrication on metal flow, thickness distribution and cavitation. It was found that reducing the interfacial friction by use of a lubricant improved the metal flow after the deformed sheet had made contact with the bottom surface of die. Changes of the metal flow during forming not only developed a better thickness distribution of the formed part, but also reduced cavitation levels.