The Effects of Sample Position and Gas Flow Pattern on the Sintering of a 7xxx Aluminum Alloy

Abstract

The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy Al-7Zn-2.5Mg-1Cu in flowing nitrogen have been investigated both experimentally and numerically. The near-surface pore distribution and sintered density of the samples show a strong dependency on the sample separation distance over the range from 2 mm to 40 mm. The open porosity in each sample increases with increasing separation distance while the closed porosity remains essentially unchanged. A two-dimensional computational fluid dynamics (CFD) model has been developed to analyze the gas flow behavior near the sample surfaces during isothermal sintering. The streamlines, velocity profile, and volume flow rate in the cavity between each two samples are presented as a function of the sample separation distance at a fixed nitrogen flow rate of 6 L/min. The CFD modeling results provide essential details for understanding the near-surface pore distribution and density of the sintered samples. It is proposed that the different gas flow patterns near the sample surfaces result in variations of the oxygen content from the incoming nitrogen flow in the local sintering atmosphere, which affects the self-gettering process of the aluminum compacts during sintering. This leads to the development of different near-surface pore distributions and sintered densities.

CFD modelling of nitrogen gas flow pattern during sintering of Al–7Zn–2.5Mg–1Cu alloy and its effect on distortion

“…It has been shown in Ref. 16 and this study that the sintering responses of samples in the same batch are closely related to the gas flow behaviour around each sample. In the following section, the new understanding gained from these two studies is applied to the sintering of an array of six samples to demonstrate an improved design process for the sintering of Al alloys.…”

“…The materials and procedures were similar to those specified in Ref. 16. All samples were made from the same elemental powder blend.…”

“…This further affects the oxygen content in local sintering atmosphere around each sample. 16 Unconstrained threedimensional (3D) CFD simulation is expected to shed more light on the effect of the nitrogen flow behaviour on the sintering of Al alloys to assist in the understanding of both of the unbalanced evaporation of Mg and Zn and differential shrinkage. This paper first presents the experimental results of the distortion and weight changes of three rectangular Al-7Zn-2.5Mg-1Cu samples, spaced 2-40 mm apart, after sintering in flowing nitrogen.…”

Distortion in a 7xxx Aluminum Alloy during Liquid Phase Sintering

“…In addition, the Reynolds number of the nitrogen flow in the furnace during sintering was only eight. [22] Hence, the temperature throughout each sample is expected to be uniform during isothermal sintering. The distortion observed is thus a consequence of other factors.…”

Sintering and Dimensional Analysis of Cu/CNTs via a Powder Metallurgy Route

“…It was observed that the effects of the sample position and different gas flow pattern near the sintering surface resulted in variations of oxygen content from the 123 incoming gas flow in the local sintering atmosphere, which affected the selfgettering process of the parts during sintering [23]. Besides that the swelling of the sample was possiblly due to gas trapped in closed pores; this would lead to an increase in internal pressure and an increase in pore size, and thus sample volume [23]. Figure 5 shows the samples for second and third trial which were sintered in two stages (refer Table 1).…”