Effect of Solidification Range on Hot Tearing Susceptibility of Al-Mg Alloys

Aluminium alloys during solidification change their density. This process can be conditionally divided into two stages: solidification shrinkage due to the density difference between liquid and solid phases and thermal contraction due to the temperature dependence of the solid density. Solidification shrinkage is the main cause of porosity in castings and also plays an essential role in the development of macrosegregation, whereas thermal contraction is important for the development of hot and cold cracks and is responsible for shape distortions during casting. An experimental technique has been developed and applied to binary Al–Cu alloys in order to quantify the thermal contraction in the solidification range and at subsolidus temperatures. It is shown that thermal contraction of aluminium alloys starts at rather high fractions of solid, between 80 and 95%. The experimentally determined temperature of contraction onset agrees well with the temperature at which the mushy material acquires the ability to transfer stresses. The magnitude of contraction accumulated in the solidification range corresponds well to hot tearing susceptibility of the alloy. Factors that decrease the temperature of contraction onset and the magnitude of contraction, e.g. grain refinement, are also known to decrease hot tearing. The data on the temperature at which the thermal contraction starts, on the magnitude of the contraction, and on the thermal contraction coefficient are used to model hot tearing and shape distortions during casting.

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Formation of the Physicomechanical Properties and Structure of Cast Al–Mg Alloys in the Solidification Range

Russian Metallurgy (Metally) ◽

10.1134/s0036029520050031 ◽

2020 ◽

Vol 2020 (5) ◽

pp. 529-535

Author(s):

E. V. Belov ◽

V. A. Duyunova ◽

A. A. Leonov ◽

A. V. Trapeznikov

Keyword(s):

Physicomechanical Properties ◽

Mg Alloys ◽

Solidification Range ◽

Al Mg Alloys

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Hot Tearing Evaluation and Contraction Behaviors of Four AA7xxx Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.817.21 ◽

2015 ◽

Vol 817 ◽

pp. 21-26 ◽

Cited By ~ 1

Author(s):

Qing Ling Bai ◽

Jun Cheng Liu ◽

Yue Li ◽

Hong Xiang Li ◽

Qiang Du ◽

...

Keyword(s):

Aluminum Alloys ◽

Hot Tearing ◽

Thermal Contraction ◽

Solidification Range ◽

Complex Interactions ◽

Zn Content ◽

Constrained Rod Casting ◽

Hot Tearing Susceptibility

The hot tearing susceptibilities (HTS) of some AA7×××alloys, AA7050, AA7055, AA7085 and AA7022 were evaluated with constrained rod casting (CRC). Thermal contraction behaviors during solidification were measured as well in a T-shaped setup. The results showed that alloys with HTS from high to low were AA7055, AA7085, AA7050 and AA7022. Zn content in 7××× aluminum alloys seemed to play a major role with respect to the HTS index. Remarkable differences could be seen on thermal contraction behaviors within solidification range for each alloy. The rate and amount of thermal contraction for AA7055 was most prominent, followed by AA7085 and AA7050, while contraction curve of AA7022 was very flat together with least amount of thermal contraction. There was a well consistency between the amount of thermal contraction and HTS. Despite complex interactions of many variables in the formation of hot tear, thermal contraction behaviors within solidification range could give a quick evaluation of hot tearing susceptibility.

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