Abstract
The effect of 0.2 wt.% Zn addition on microstructure, age hardening and intergranular corrosion (IGC) properties of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, hardness testing, and electrochemistry testing. The results showed that the addition of Zn can accelerate the transformation of GP zones into β″, and make the intragranular precipitates become smaller and with higher density. This is beneficial to the precipitation strengthening of the alloy, leading to obtaining higher hardness and enhancing the age hardening response. The peak hardness of the alloy with the addition of Zn is 125.8 HV which means increasing the hardness by 12.7 HV, compared with the alloy without Zn. However, the addition of Zn makes the precipitate-free zone (PFZ) of the alloy wider, and coarsens the grain boundary precipitates slightly, which result in the reduction of IGC resistance of Al-Mg-Si alloy. The maximum corrosion depth of the Zn-containing alloy is 121.3 μm in the peak age condition, which is 35.7 μm deeper than the alloy without Zn. The result of the potentiodynamic polarization curves also demonstrated the increase of IGC sensitivity. The corrosion current density of the alloy with added Zn is 0.595 μA/cm2 in the peak age condition, while that for the alloy without Zn is 0.199 μA/cm2.
Highlights
As heat-treatable alloys, Al-Mg-Si alloys have been widely used in automobile manufacturing, and have become the preferred material for automobile body plate, due to their high specific strength, good formability, excellent corrosion resistance, and weldability [1,2]
AA and AZAccording to the measured width of the precipitate-free zone (PFZ), we found that the PFZ of alloy AA and AZ all became wider with the AA AA, the PFZ of alloy AZAlloy increase of aging time
According to the measured width of the PFZ, we found that the PFZ of alloy AA and AZ all became wider with the increase of aging time
Summary
As heat-treatable alloys, Al-Mg-Si alloys have been widely used in automobile manufacturing, and have become the preferred material for automobile body plate, due to their high specific strength, good formability, excellent corrosion resistance, and weldability [1,2]. These alloys are still face some challenges regarding their application, such as how to further improve their corrosion resistance, moldability, and get a quick age hardening response after a short-time paint baking [3]. It was shown in [7] that the Al-Mg-Si-Cu alloys
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