Hot Tearing Evaluation and Contraction Behaviors of Four AA7xxx Alloys

2015 ◽  
Vol 817 ◽  
pp. 21-26 ◽  
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.

Thermal Contraction during Solidification of Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1681-1686 ◽  
Author(s):  
Dmitry G. Eskin ◽  
Laurens Katgerman
Keyword(s):  
Aluminium Alloys ◽  
Hot Tearing ◽  
Thermal Contraction ◽  
Solidification Shrinkage ◽  
Solidification Range ◽  
Cu Alloys ◽  
Solid Density ◽  
Two Stages ◽  
Liquid And Solid Phases ◽  
Hot Tearing Susceptibility

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.

scholarly journals Effects of Zn content on Hot Tearing Susceptibility of Mg–7Gd–5Y–0.5Zr Alloy

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 414
Author(s):  
Ziqi Wei ◽  
Shimeng Liu ◽  
Zheng Liu ◽  
Feng Wang ◽  
Pingli Mao ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Parent Phase ◽  
Hot Tearing ◽  
Shrinkage Stress ◽  
Second Phase ◽  
Residual Liquid ◽  
Long Period ◽  
Zn Content ◽  
Feeding Effect ◽  
Hot Tearing Susceptibility

Mg–7Gd–5Y–0.5Zr alloy has excellent mechanical properties but poor hot tearing resistance. The latter makes it difficult to cast billets, which limits the size of subsequently processed parts. Therefore, the hot tearing susceptibility of Mg–7Gd–5Y–xZn–0.5Zr (x = 0, 3, 5, 7 wt%) alloys was studied. It was found that Zn can significantly reduce hot tearing susceptibility of Mg–7Gd–5Y–0.5Zr alloy, which almost linearly decreased with Zn content. When Zn content was 3 wt%, 5 wt% and 7 wt%, hot tearing susceptibility will be reduced by 27%, 83% and 100%, respectively. It was further revealed that the solid solubility of Gd and Y in α-Mg decreased with the increase of Zn content, and the nucleation temperature decreased accordingly, which resulted in the increase of nucleation rate and the refinement of final grains. On the macro level, it showed that the dendrite coherency temperature decreased, the solidification shrinkage stress of α-Mg slowed down, and the residual liquid channel became shorter and hot tearing susceptibility decreased. It was also found that with the increase of Zn content, the content of Zn, Gd and Y enriched on the grain boundary increased, the content of residual liquid phase between dendrites increased after α-Mg crystallization, and the solidified precipitated second phase also changed from Mg5RE phase to long-period stacking ordered phase + W-phase (a little), long-period stacking ordered phase + W-phase (much) and finally to W-phase only. The feeding effect of sufficient intergranular residual liquid on the shrinkage of α-Mg dendrite and the bridging effect of the precipitated phase at the grain boundary (especially long-period stacking ordered phase which is coherent with the parent phase) also led to the decrease of hot tearing susceptibility.

Effects of Zn Content on Hot Tearing Susceptibility of Mg–Zn–Gd–Y–Zr Alloys

2022 ◽  
Author(s):  
Ziqi Wei ◽  
Shimeng Liu ◽  
Zheng Liu ◽  
Le Zhou ◽  
Yan Li ◽  
...  
Keyword(s):  
Hot Tearing ◽  
Zn Content ◽  
Hot Tearing Susceptibility ◽  
Zr Alloys

Effect of Structure on Hot Tearing Properties of Aluminum Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 995-998 ◽  
Author(s):  
Dmitry G. Eskin ◽  
Laurens Katgerman
Keyword(s):  
Aluminum Alloys ◽  
Solid Phase ◽  
High Strength ◽  
Direct Chill ◽  
Hot Tearing ◽  
Direct Chill Casting ◽  
Small Scale ◽  
Thermal Contraction ◽  
Chill Casting ◽  
High Strength Aluminum Alloys

Hot tearing is a significant problem upon direct-chill casting of high-strength aluminum alloys. The occurrence of hot cracks is related to the thermal contraction of the solid phase and to the lack of feeding by the liquid phase during solidification. It has been identified that structure features such as grain size and amount of nonequilibrium eutectics influence both phenomena involved in hot tearing. Experimental and computer-simulation results are presented for a range of model and commercial aluminum alloys. The results are obtained both during special small-scale experiments and during industrial-scale direct-chill casting. It is shown that grain refinement reduces hot tearing susceptibility of aluminum alloys through the related decrease of the temperature of thermal contraction onset and increased permeability of the mushy zone. The effects of process parameters on hot tearing are also discussed.

Hot Tearing Susceptibility and Fluidity of Semi-Solid Gravity Cast Al-Cu Alloy

2006 ◽  
Vol 116-117 ◽  
pp. 76-79 ◽  
Author(s):  
J. Wannasin ◽  
David Schwam ◽  
J.A. Yurko ◽  
C. Rohloff ◽  
G. Woycik
Keyword(s):  
Liquid State ◽  
Copper Alloys ◽  
High Strength ◽  
Hot Tearing ◽  
Gravity Casting ◽  
Aluminum Copper Alloys ◽  
Semi Solid ◽  
High Superheat ◽  
Constrained Rod Casting ◽  
Hot Tearing Susceptibility

Aluminum-copper alloys offer both high strength and excellent ductility suitable for a number of automotive applications to reduce vehicle weight; however, the alloys are difficult to cast because of their tendency for hot tearing. In this work, semi-solid gravity casting of an aluminum-copper alloy, B206, was conducted in constrained rod casting molds to study the feasibility of using the process to reduce or eliminate hot tearing. To demonstrate the feasibility of gravity casting of the metal slurries, a fluidity test was also conducted. Results show that the hot tearing susceptibility of the aluminum-copper B206 alloy cast in semi-solid state is lower than those cast in liquid state with high superheat temperatures. The grain size of the semi-solid cast Al-Cu samples appears to be finer than those cast in liquid state with high superheat temperatures. In addition, the metal slurries had sufficient fluidity to fill the molds even with low gravity pressures. The results suggest that semi-solid gravity casting is a feasible process to help reduce hot tearing.

Roles of Alloy Composition and Grain Refinement on Hot Tearing Susceptibility of 7××× Aluminum Alloys

2016 ◽  
Vol 47 (8) ◽  
pp. 4080-4091 ◽  
Author(s):  
Q. L. Bai ◽  
Y. Li ◽  
H. X. Li ◽  
Q. Du ◽  
J. S. Zhang ◽  
...  
Keyword(s):  
Aluminum Alloys ◽  
Grain Refinement ◽  
Alloy Composition ◽  
Hot Tearing ◽  
Hot Tearing Susceptibility

scholarly journals Influences of Y Additions on the Hot Tearing Susceptibility of Mg-1.5wt.%Zn Alloys

2013 ◽  
Vol 765 ◽  
pp. 306-310 ◽  
Author(s):  
Zhi Wang ◽  
Yuan Ding Huang ◽  
Amirthalingam Srinivasan ◽  
Zheng Liu ◽  
Karl Ulrich Kainer ◽  
...  
Keyword(s):  
Grain Size ◽  
Data Acquisition System ◽  
Hot Tearing ◽  
Mould Temperature ◽  
Crack Volume ◽  
Coarse Microstructure ◽  
Constrained Rod Casting ◽  
Equiaxed Grain ◽  
Zn Alloys ◽  
Hot Tearing Susceptibility

The influences of Y (0.2, 2 and 4 wt.%) additions on the hot tearing behaviour of Mg‑1.5Zn alloys were investigated using a constrained rod casting (CRC) apparatus equipped with a load cell and data acquisition system. The initiation of hot tearing was monitored during CRC experiments. It corresponds to a drop in load on the hot tearing curves. The experimental results indicate that, the hot tearing susceptibility defined by the total crack volume, which was measured by the wax penetration method, decreases with increasing the content of Y at a mould temperature of 250 °C. The reduced susceptibility is attributed to the effect of Y on the solidification behaviour: it shortens the freezing range and reduces the grain size. The highest susceptibility is observed for Mg-1.5Zn-0.2Y alloy. It is caused by its coarse microstructure and relatively larger solidification range. In contrast, the lowest susceptibility is observed for Mg-1.5Zn-4Y alloy with a small equiaxed grain microstructure. In addition, the healing of hot cracks by the subsequent refilling of the remained liquid at the later stage of solidification is also beneficial for the alleviation of hot tearing susceptibility in Mg-1.5Zn-4Y alloy.

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