Abstract: Alternating current field enhanced pack boron-aluminizing (ACFPBA)in which the inward diffusion of boron dominated was carried out at 750 ℃ with different pack agent. By observing and analyzing the case microstructure, phase, thickness and microhardness distribution along the depth of cases, it is found that the aluminium powder in the agent can promote the ACFPBA. The promotion extent is related not only with the Al content in the agent, but also with the ferroboron content. When the optimum aluminium powder content is employed, the promotion effect with agent containing lower ferroboron content is better than that with agent containing higher ferroboron content. An ACF enhanced boriding case with Fe₂B single-phase is obtained with agent containing lower ferroboron content. However, adding more than 0.5% aluminium powder to the agent, the obtained case is composed of duplex-phase of FeB and Fe₂B. And the hardness of the near surface region is increased. When other treating parameters are the same, adding 1% aluminium powder into the agent containing 6% ferroboron leads to an about 70 μm thick case after 4 h ACFPBA and the case's hardness curve distributes more gently. However, the case thickness by corresponding ACF enhanced boriding is only about 26 μm.

Key words: pack boron-aluminizing, alternating current field, microstructure, phase, microhardness