Papers by Keyword: Pre-Deformation

Abstract: In the present research, the fatigue crack growth (FCG) of AISI 1020 steel with and without pre-deformation were characterized by using MTS Landmark 100 kN under fatigue loading at ratio (R) = 0.3, P_max = 0.7 and f = 10 Hz at room temperature. Tensile test results show that 6.25% pre-deformation given on the steel increases of yield strength. In contrast, the ultimate tensile strength, elastic modulus and elongation decrease. The FCG rate (da/dN) of AISI 1020 steel without pre-deformation determined at stage II is 6.12´10^-11ΔK^2.94 m/cycle and steel with 6.25% pre-deformation is 8.03´10^-10ΔK^2.02 m/cycle. According to microstructural observation for the pre-deformation steel, plastic deformation formed on the steel in the axial direction affects the FCG rate of the steel, leads to crack retardation for certain period of time. SEM fractographic observation on the fracture surface of the steel shows that a transgrannular crack length of 12 mm for 42,000 cycles occurs at ferrite grains. The steel failed when the crack length reached ~18.1 mm within 43,500 cycles and continuing up to 43,549 cyles, the steel experienced static failure.

Abstract: Pre-deformation is usually indispensable to obtain an appropriate balance between microstructure and mechanical properties of Al-Cu-Li alloys. In this paper, the effect of pre-deformation degree on the evolution of strength, fracture toughness, and precipitates during artificial aging processes of a novel Al-Cu-Li alloy was studied. The results indicated that the amount of T₁ phase increased remarkably while the precipitation of θ' phase was inhibited with the increase of pre-deformation degree. The change in the average size of T₁ phase indicated that the increase in nucleation sites suppressed the full growth of T₁ phases. The fracture toughness could be related to the strength difference between intragranular and intergranular. Based on the matching of properties, a reasonable pre-deformation parameter was proposed.

Abstract: In the present work, the effects of pre-deformation before aging on the precipitation phase and mechanical properties of a new type X2A66 alloy was investigated with the help of the room temperature tensile test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. The experimental research results prove that reducing the aging temperature or pre-deformation before aging is beneficial to improve the mechanical properties of the alloy. Compared with decreased aging temperature, pre-deformation treatment before aging can significantly improve the mechanical properties of the alloy, and its yield strength (YS), ultimate tensile strength (UTS) and elongation are 593.4Mpa, 610.8Mpa, and 10.7%, respectively.

Abstract: Predeformation on tensile properties and microstructure of three Al-Cu-Li alloys, 1460, 2050 and 2A96 was investigated. The strength of the alloys is enhanced by the predeformation. Meanwhile, predeformation impacts the precipitation of T1 (Al₂CuLi) and θ′(θ′′) (Al₂Cu) phases. The precipitation (nucleation rate) of T1 is accelerated by the predeormation, and the effect is increased with the predeformation degree. While, effect on θ′(θ′′) precipitation is dependent on the alloy composition feature. In the 2A96 alloy with a medium Cu/Li ratio, it is decelerated by the predeformation. In the 2050 alloy with high Cu/Li ratio and 1460 alloy with low Cu/Li ratio but subjected to two-step aging at 130°C and 160°C, the θ′(θ′′) precipitation is accelerated at lower predeformation but decelerated at higher predeformation.

Abstract: Semi-solid billet of ZCuSn10 (Wt%: 88.25Cu, 10.48Sn) alloy is prepared by strain induced melt activated (SIMA) method which including rolling and remelting process. Firstly, ZCuSn10 alloy is casted, and rolling samples are cut from ingot casting. Secondly, the rolling samples are two pass or four pass rolled after holding 15 minutes at 450°C, then samples with 10% and 20% pre-deformation degree are obtained. The remelting samples are cut from pre-deformed samples. Lastly, the remelting samples are reheated up to 850°C or 875°C, water quenching after holding for 15 minutes. Then semi-solid microstructure of ZCuSn10 alloy is prepared. The semi-solid microstructure of ZCuSn10 alloy is observed and compared with annealed microstructure and microstructure of ZCuSn10 alloy directly remelted after casting. The results indicate that semi-solid microstructure of ZCuSn10 alloy by rolling-remelting SIMA process is uniform and fine grain, and spheroidization level of solid particle is well. The optimum semi-solid microstructure is obtained when alloy with pre-deformation 20% is remelted at 875°C for 15 minutes, the average grain diameter is about 75.80μm, shape factor is 1.62, and volume fraction of liquid phase reaches about 17.28%. Pre-deformation process plays a crucial role in grain refinement and spheroidization during SIMA process for preparing the semi-solid ZCuSn10 alloy, as pre-deformation degree and remelting temperature increases, volume fraction of liquid phase increases, the solid particles in semi-solid microstructure are smaller and rounder. The main mechanism of SIMA process preparing semi-solid billet of ZCuSn10 alloy is that pre-deformation breaks dendrites and stores energy of deformation into alloy, and promotes dendrites fusing through remelting process. Meanwhile, liquid phase occupies sharp corners of solid particles by Sn element diffusing from liquid phase into α solid phase, so that fine and uniform and globular α solid particles are gained.

Abstract: Effects of mechanical treatment, pre-strain and pre-deformation temperature on shape recovery stress of Ti₅₀Ni₄₇Fe₃ shape memory alloys were investigated. Mechanical treatment, consisting of hot-rolling and hot-forging, improved σrmax σrmax (maximum recovery stress), dσr/dT (rate of recovery stress with temperature) and T_s (the temperature at which recovery stress rises sharply). Martensitic transformation and reverse transformation temperatures also increased with increasing the hot-rolling deformation. σrmax and dσr/dT increased with increasing pre-strain at first and then decreased with further increasing of pre-strain, and the maximum values of σrmaxand dσr/dT were obtained at a pre-strain of 10%. On the other hand, σrmaxand dσr/dT decreased with increasing pre-deformation temperature. Upon a hot-rolling of 88% area reduction and pre-deformation of 10% at-150°C, the Ti₅₀Ni₄₇Fe₃ alloy exhibited excellent recovery stress property with the σrmax of 391MPa in combination with dσr/dT of 5.09.

Abstract: In the present work we report on the effect of pre-deformation followed by/together with artificial aging on the mechanical properties as strength, ductility and work hardening of an Al-Mg-Si alloy (AA6060). The AA6060 alloy was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificially aged after (sequential mode) and during (simultaneous mode) various combinations of deformation (0-10%) and heat treatments. The aging behaviour and mechanical properties have been characterized in terms of Vickers hardness and tensile testing. It is found that small, even very small, pre-deformations strongly affect the aging behaviour and associated tensile properties. Moreover, it is found, that with the carefully chosen parameters of simultaneous deformation and aging one can reach mechanical properties superior to those following pre-deformation and subsequent aging (sequential mode). The results are compared and discussed in view of differences in processing conditions and microstructure characteristics.

Abstract: The present paper reports on the fatigue response of a commercial high manganese steel that features the twinning-induced plasticity (TWIP) effect in the high-cycle fatigue (HCF) regime. Specifically, attention was paid to the influence of the degree of pre-deformation and notches on the damage initiation and propagation in the TWIP steel studied. As monotonic pre-deformation significantly increases the fraction of twins and concomitant the strength of the steel, the fatigue properties and notch sensitivity are altered drastically. A thorough experimental approach including mechanical testing and microstructural characterization was employed to shed light on the microstructure-mechanical properties-relationships in order to deepen the understanding of the critical damage mechanisms. The current study clearly lays out that competing mechanisms effect the fatigue response of the TWIP steel, i.e. pre-deformation leads to strengthening but also induces damage. Since both effects evolve differently upon pre-deformation, fatigue performance can be optimized by appropriate amounts of pre-deformation.

Abstract: During the indirect hot stamping process of boron steel, the pre-deformed component undergoes air cooling, one-side-contact cooling and both-side-contact cooling phases successively. The effects of pre-deformation and cooling rate on the phase transformation should be understood before conducting indirect hot stamping experiments of vehicle components. Uniaxial tensile tests of boron steel at RT were carried out to obtain specimens with different pre-strain levels. Then they were heated to 900°C according to the indirect hot stamping process and quenching tests were performed on them at different cooling rates. Metallographic observations were performed on the quenched specimens and their hardness was measured. The results show that the pre-strain at RT has little influence on the phase transformation of boron steel. This is due to the dislocation structure introduced by deformation at RT recovered during the heating process and it is good for the indirect hot stamping. Upper B-pillar parts were first cold pre-formed, and then were heated and hot stamped. The microstructure and hardness results at different locations on the indirect hot stamped components are demonstrated qualified.

Abstract: Warm deep drawing processing was used to improve the deep drawability of Twin Roll Cast AZ31B magnesium sheet. Conspicuous effects were obtained and the Limited Drawing Ratio value of the sheet was improved by about 50% after the pre-deformation. Influence factor on the drawability of Twin Roll Cast magnesium alloy sheet was also analyzed. Numerical simulation method and microstructure analysis method were used to discuss the mechanisms of formation and develop of Twin Roll Cast microstructure in the twin roll cast process and the pre-deformation process.