| Aluminium alloy has become the optimal material of choice for the "lightweighting" of vehicle. The Al-Mg-Si alloy has been widely used in automotivestructural design for energy absorption due to its excellent collision energy absorptionperformance and formability. In this paper, the aging hardening properties of6061Xaluminium alloy, and the deformation modes and energy absorption capacities of6061X profiles and6061profiles under axial compression were investigated. The mainreason for the performances difference of the two alloys was also explored incombination with micro-analysis.The6061X alloy was firstly exposed to various aging condition (at140℃-220℃for0-24h) and the effect of aging temperature and time on mechanical properties wasinvestigated by hardness tests. The results show that the maximum hardness of6061Xalloy could be achieved by aging at180℃for9h. The needle-shaped β"precipitateswere observed in the aged alloy with peak hardness by TEM analysis. Moreover, on thebasis of Johnson-Mehl-Avrami equation, an aging kinetics model of6061X alloy wasderived by regression analysis.The deformation modes and energy absorption capacities of6061X alloy and6061alloy were researched by quasi-static axial compressions. The two kinds of Al-Mg-Sialloy were respectively aged at temperature of180℃from30min to540min. Theresults indicate that the deformation mode of the6061X profiles is gradually changedfrom "Diamond mode" to "Concertina mode", while the6061profiles is changed from"Diamond mode" with cracking phenomenon to "splitting mode" along the edge of theprofile, and both the energy absorption of the two kinds of extrusions increased withincreasing aging time. Drilling holes on the sidewalls near the upper end of the profilescan decrease the peak load and change the deformation mode of the6061X profiles andthe6061profiles into "Mixed mode" or "Concertina mode" and "Mixed mode" withcracking phenomenon respectively, which improves the stability of sample duringdeformation. As to samples with diamond mode before drilling holes, mean load of thesamples during deformation increases and energy absorption are improved afterdrilling induced holes. On the contrary，the energy absorption of samples with mixedmode or concertina mode reduces after drilling holes.The microstructure and properties of6061alloy and6061X alloy were studied comparatively. The results show that the distribution of grains in the6061alloy isinhomogeneous along the thickness direction. Coarse recrystallization grains wereobserved in the near-surface layer, while elongated grains including subgrains wereobserved in the center layer. Moreover, the grains in the6061alloy tended to alignalong {111} crystal plane, and the second-phase particles were arranged alongextrusion direction. However, complete recrystallization grains were observed in the6061X alloy, and the degree of preferred orientation of the grains was lower comparedwith the6061alloy. The inhomogeneous distributions of grainmorphology,crystallographic orientation and the second-phase particles in the6061alloy, cause asignificant anisotropy of the mechanical properties, leading to the transverse crack ofthe6061alloy when bending. Therefore, it is reasonable to reduce the anisotropy ofthe mechanical properties of the alloy by improving its recrystallization degree. |
PDF Full Text Request