The influence of process parameters on the preparation of closed-cell aluminum foam by friction stir processing

Abstract

In order to obtain high-quality aluminum foam components, a new preparation method for a 7075 closed-cell aluminum foam based on friction stir processing (FSP) was proposed. The influence of process parameters on microstructures of closed-cell Al foam precursor was investigated by optical metallographic microscope and scanning electronic microscope (OM/SEM). The temperature field and flow field of the Al foam precursor during FSP were simulated by Fluent CFD software. The formability of the Al foam precursor was analyzed by the cupping test. It is found that the rotating speed has great influence on the uniformity and density of the precursor prepared by FSP, but the welding speed has little influence. Numerical simulation shows that the maximum flow velocity of material in the tool shoulder increases by 1.5 times when the rotating speed increases from 800 to 2000 r/min, and the peak temperature at the stirring pin reaches 491 °C, which is consistent with the experimental results. The powder ring is continuous and uniform due to sufficient plastic deformation and flow at travel speed of 50 mm/min and the rotating speed of 2000 r/min. The formability of the precursor increases with the increase of deformation temperature. Especially the cupping test value of precursor is close to that of base metal at 450 °C. In the foaming process, the foam pores first appear at the bottom and then expand upwards with the extension of the foaming time. The expansion rate of the whole foam increases rapidly, and the pores with highly spherical are homogeneously distributed when the foaming time is 110 s at 680 °C.