Abstract
Severe hot tearing has been observed during DC casting of modified AA3000 alloys with additions of Cu, Ti, and Zr, although these alloys are regarded as rather easy to cast. Extensive studies have been performed on both synthetic and industrial AA2000, AA6000, and AA7000 alloys, but less data are available for AA3000 alloys. This work was thus initiated to investigate the hot tearing susceptibility of AA3000 alloys with varying alloy element content using constrained rod casting molds. The results showed that the Cu and Fe content have a major impact on hot tearing resistance, while the effects of Zr and Ti are minor. Cu in a range from 0.3 to 1.2 wt pct significantly increased the hot tearing tendency. This is due to the existence of high eutectic fractions at low temperatures, as well as porosity formation associated with bad feeding at the end of solidification. A strong cracking tendency was observed below an Fe content 0.2 wt pct owing to decreased precipitation of the Al6(Mn, Fe) phase. It was found that primary Al6(Mn, Fe) phases lead to early bridging between the grains, which reinforces the alloy during the vulnerable temperature range for hot tearing. Zr and Ti additions weakly enhanced or reduced hot tearing severity, respectively.
Highlights
HEAT exchangers are an important application of direct chill (DC) cast rolling ingots produced from AA3000 Al alloys
To optimize the material properties for these applications, copper alloying is common, as well as minor additions of titanium and zirconium. These additions are mainly made to improve the corrosion properties, which is very important for automotive heat exchangers, but the modifications have resulted in a marked increase in hot tearing tendency, which differs from what had previously been experienced for AA3000 alloys with regular compositions
Hot tearing susceptibility (HTS) has been associated with factors such as the solidification interval, microstructure development, eutectic feeding ability, and stress–strain induced during solidification.[1,4,5,26]
Summary
HEAT exchangers are an important application of direct chill (DC) cast rolling ingots produced from AA3000 Al alloys. To optimize the material properties for these applications, copper alloying is common, as well as minor additions of titanium and zirconium These additions are mainly made to improve the corrosion properties, which is very important for automotive heat exchangers, but the modifications have resulted in a marked increase in hot tearing tendency, which differs from what had previously been experienced for AA3000 alloys with regular compositions. Hot tearing is a serious defect that occurs during the solidification of Al alloys in DC casting It is an irreversible failure, which starts forming during the semi-solid stage of solidification and eventually shows up as a crack either on the surface or inside the solidified ingots.
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