Papers by Keyword: AA5754

Abstract: To address the challenges of reducing the CO₂ emission in automotives, Aluminum metal matrix hybrid composites have been extensively used in automotive and aerospace industries for the fabrication of light weight structure. Huge demand in joining dissimilar metals increased day by day, because it reduces the weight and cost of components by utilizing hybrid structures. The friction stir welding is adopted for dissimilar AA5754 rheo-squeeze cast (RSC) with AA7075 stir casted hybrid composite. Micro sized B₄C and nanosized Al₂O₃ are reinforced into this material. Friction stir welding of these alloys by varying the tool material, pin and shoulder profiles, rotational speed, tool traverse speed and tilt angle. Microstructure of the joint are studied and inferences drawn are presented. The better welding was obtained with triangular and square pin profile when compared to cylindrical pin whereas triangular pin profile was more better than square pin. Tapered shoulder possessed greater strength, which resulted in a good weld in contrast to flat shoulder. The high carbon high chromium steel (HCHCr) tool exhibited a higher tool wear rate than stainless steel (SS) tool and found to be an appropriate one to weld aluminum hybrid composite.

Abstract: In this work, the hydroforming process in warm conditions was used for manufacturing an Al-Mg alloy (AA5754) benchmark component displaying different strain levels due to its geometry. The attention was focused on the effect of the rate to increase the forming pressure (PR), strictly related to the strain rate the material is subjected to. In fact, preliminary tensile and Nakajima tests (both at room temperature and in warm conditions) revealed that the mechanical and formability properties of the investigated alloy are strongly affected by the strain rate. Warm Hydroforming tests were conducted in order to investigate both the working temperature and the parameter PR. The Blank Holder Force profile was varied according to an experimentally determined profile able to avoid oil leakages. Experimental results were collected in terms of output variables related to the die cavity filling and to the strain level reached on the component: in such a way a multi-objective optimization could be carried out using the commercial integration platform modeFRONTIER. The best compromise between the high level of the component deformation and the cycle time could be obtained by conducting the warm hydroforming process at the temperature of 250°C and setting the parameter PR equal to 0.1 MPa/sec.

Abstract: An FE model for the hot forming and cold-die quenching (HFQ) process was developed. This model was verified by HFQ experiments through a comparison of the thickness distribution between the simulated and experimental results; good correlation with a deviation of less than 5% was achieved. In addition, this FE model was used to study the effects of forming speed on the thickness distribution of a HFQ formed part, and it was found that a higher forming speed is beneficial for HFQ forming, as it led to improved thickness homogeneity and less thinning.

Abstract: Two AA5754 sheets have been processed by cold rolling with 83% thickness reduction, one at room temperature and another with liquid nitrogen as coolant. The sheets were subsequently annealed at 220-275°C for 1 hour. The development of grain structure and texture was studied by optical microscope, scanning electron microscopy (SEM), X-ray diffraction and electron backscatter diffraction (EBSD) in SEM, and the mechanical property by micro-hardness testing. It has been demonstrated that the as-rolled sheets have the same micro-hardness, but the grain structures and textures are very different. Compared to the sheet processed with liquid nitrogen, the one rolled at room temperature has stronger shear texture and finer grain structure.

Abstract: Al alloys with Mg as the major alloying element constitute a group of non-heat treatable alloys with medium strength, high ductility, excellent corrosion resistance and weldability. However, the segregation of Mg may adversely affect the performance of these materials if they are exposed to rapid heating and cooling environments such as resistance spot welding. The formation and migration of vacancy is an important factor affecting Mg segregation. In this paper, the amount and distribution of Mg were measured by electron probe microanalysis and the vacancy formation energy in AA5754 alloys was measured by positron annihilation lifetime spectroscopy. The results indicated that the segregation of Mg at cracks, occurring under suitable temperature and stress conditions, is related to the formation and migration of vacancies, and may promote crack initiation and propagation.

Abstract: A number of mechanical tests and metallographic techniques have been used to investigate the mechanism of ductile fracture of AA5754 sheet. The sequence of events in the development of shear localization is clarified using in situ strain mapping on both the sample surface and through thickness direction during tensile tests. It is observed that the failure mode changes from cup-cone type to shearing with increasing Fe content in both continuous cast (CC) and direct-chill cast (DC) AA5754 sheets. However, this transition happens in CC with much lower Fe content than DC. As very little damage is found near the fracture surface, this suggests that damage may be a consequence of the shear process rather than a trigger that determines material ductility. For both CC and DC with same Fe content of 0.21%, fracture strain of CC is much lower than DC. It is postulated that this is due to the differences of particle distribution in these two materials, especially the increased fraction of stringer type structures which exist in CC material.

Abstract: Accumulative Roll Bonding (ARB) is a technique of grain refinement by severe plastic deformation, which involves multiple repetitions of surface treatment, stacking, rolling, and cutting. The rolling with 50% reduction in thickness bonds the sheets. After several cycles, ultrafine-grained (UFG) materials are produced. Since ARB enables the production of large amounts of UFG materials, its adoption into industrial practice is favoured. ARB has been successfully used for preparation of UFG sheets from different ingot cast aluminium alloys. Twin-roll casting (TRC) is a cost and energy effective method for manufacturing aluminium sheets. Fine particles and small grain size are intrinsic for TRC sheets making them good starting materials for ARB. The paper presents the results of a research aimed at investigating the feasibility of ARB processing of three TRC alloys, AA8006, AA8011 and AA5754, at ambient temperature. The microstructure and properties of the ARB were investigated by means of light and transmission electron microscopy and hardness measurements. AA8006 specimens were ARB processed without any problems. Sound sheets of AA8011 alloy were also obtained even after 8 cycles of ARB. The AA5754 alloy suffered from severe edge and notch cracking since the first cycle. The work hardening of AA8006 alloy saturated after the 3rd cycle, whereas the hardness of AA5754 alloy increased steadily up to the 5th cycle. Monotonous increase in strength up to 280 MPa was observed in the ARB processed AA8011 alloy.

Abstract: This paper addresses the effect of microstructure on the formability of aluminium alloys of interest for automotive sheet applications. The bulk of this work has been on the alloy AA5754 – both conventional DC cast alloys and continuous cast alloys made by twin belt casting. It is known that alloys such as these contain Fe as a tramp impurity which results in Fe-based intermetallic particles distributed through microstructure as isolated particles and in stringers aligned along the rolling direction. It is thought that these particles are the cause, both of the reduced ductility that is observed as the Fe level rises, and the relatively poor formability of strip cast alloys, as compared with those made by DC cast. Conventional wisdom suggests that the reduction of ductility is due to the effect of particles as nucleating sites for damage. However, most studies show that these materials are resistant to damage until just before fracture. We now believe that effect is actually related to the development of shear bands in these materials. We present experimental data which supports this conclusion. We then show how the FE models we have developed demonstrate the role of shear instability on fracture and the role played by hard particles. We show how a unit cell approach can be used to incorporate the effect of particle density and morphology on shear localization in a way that includes statistical variability due to microstructural heterogeneity. This leads to a set of constitutive equations in which the parameters are distributed from one region to another. These are then fed into a macroscopic FE model at the level of the specimen or the component in order to determine the effect of microstructural variability on shear instability and ductility.

Abstract: This paper presents results from quasi-static and high rate tensile testing of three aluminum sheet alloys, AA5754, AA5182 and AA6111, all of which are candidates for replacing mild steel in automotive bodies. Tests were performed at quasi-static rates using an Instron apparatus and at strain rates of 600 to 1500 s-1 using a tensile split Hopkinson bar. Additionally, an in-depth investigation was performed to determine the levels of damage within the materials and its sensitivity to strain rate. The constitutive response of all of the aluminum alloys tested showed only mild strain rate sensitivity. Dramatic increases in the elongation to failure were observed with increases in strain rate as well as greater reduction in area. Additionally, the level of damage was seen to increase with strain rate.