Hot Tear Susceptibility of Al-Mg-Si-Fe Alloys with Varying Iron Contents

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 Al 6 (Mn, Fe) phase. It was found that primary Al 6 (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.

Section: Introductionmentioning

confidence: 99%

“…Better interdendritic liquid feeding during shrinkage allows the cracks to heal (second half of lambda curve). [1,3,4] Chemical composition can also influence the hot tearing resistance of alloys by changing the morphology, precipitation, and grain size. However, contradictory results related to hot tearing have been reported.…”

Section: Introductionmentioning

confidence: 99%

Hot Tearing Susceptibility of AA3000 Aluminum Alloy Containing Cu, Ti, and Zr

Razaz

Carlberg

2019

“…However, there is limited information on the effect of constitutive phases such as Fe-rich intermetallics on the semisolid tensile properties of aluminum alloys during the last stage of solidification. The morphology, size and distribution of these intermetallics are important for the formation of casting defects such as hot tearing [28,31].…”

Section: Introductionmentioning

confidence: 99%

“…[39,40]. In addition to affecting the mechanical properties of Al-Cu 206 alloys at ambient temperature, these intermetallics may also significantly influence the semisolid tensile properties of the mush [31].…”

Section: Introductionmentioning

confidence: 99%

Effects of Iron-Rich Intermetallics and Grain Structure on Semisolid Tensile Properties of Al-Cu 206 Cast Alloys near Solidus Temperature

Bolouri

Liu

Chen

2016

The effects of iron-rich intermetallics and grain size on the semisolid tensile properties of Al-Cu 206 cast alloys near the solidus were evaluated in relation to the mush microstructure.Analyses of the stress-displacement curves showed that the damage expanded faster in the mush structure dominated by plate-like β-Fe compared to the mush structure dominated by Chinese script-like α-Fe. While there was no evidence of void formation on the β-Fe intermetallics, they blocked the interdendritic liquid channels and thus hindered liquid flow and feeding during semisolid deformation. In contrast, the interdendritic liquid flows more freely within the mush structure containing α-Fe. The tensile properties of the alloy containing α-Fe are generally higher than those containing β-Fe over the crucial liquid fraction range of ~0.6 to 2.8%, indicating that the latter alloy may be more susceptible to stress-related casting defects such as hot tearing. A comparison of the semisolid tensile properties of the alloy containing α-Fe with different grain sizes showed that the maximum stress and elongation of the alloy with finer grains were moderately higher for the liquid fractions of ~2.2-3.6%. The application of semisolid tensile properties for the evaluation of the hot tearing susceptibility of experimental alloys is discussed.2

“…This model has been validated in a number of aluminum alloy systems. [6][7][8][9][10] The RDG model attributes the formation of hot cracking to two main factors: lack of liquid feeding; and tensile deformation in the coherent dendritic network caused by thermal contraction of the solid. This model is based on the observation that hot cracking occurs in the vulnerable mushy zone when the material is at a temperature between the coherency temperature and solidus.…”

Section: Introductionmentioning

confidence: 99%

Process Optimization of Dual-Laser Beam Welding of Advanced Al-Li Alloys Through Hot Cracking Susceptibility Modeling

Tian

Robson

Riekehr

et al. 2016

Laser welding of advanced Al-Li alloys has been developed to meet the increasing demand for light-weight and high-strength aerospace structures. However, welding of high-strength Al-Li alloys can be problematic due to the tendency for hot cracking. Finding suitable welding parameters and filler material for this combination currently requires extensive and costly trial and error experimentation. The present work describes a novel coupled model to predict hot crack susceptibility (HCS) in Al-Li welds. Such a model can be used to shortcut the weld development process. The coupled model combines finite element process simulation with a two-level HCS model. The finite element process model predicts thermal field data for the subsequent HCS hot cracking prediction. The model can be used to predict the influences of filler wire composition and welding parameters on HCS. The modeling results have been validated by comparing predictions with results from fully instrumented laser welds performed under a range of process parameters and analyzed using high-resolution X-ray tomography to identify weld defects. It is shown that the model is capable of accurately predicting the thermal field around the weld and the trend of HCS as a function of process parameters.