Healing of double oxide film defects in A356 aluminium melt

Effect of Ca on the Behavior of Double Oxide Film Defects in Commercially Pure Aluminum Melt

“…Aryafar et al [7] showed that after O and N of the trapped atmosphere within a defect that was held in an A356 aluminum melt was consumed, the two oxide layers of the defect gradually bonded with each other during the transformation of Al 2 O 3 to MgAl 2 O 4 and then to MgO. The occurrence of such bonding (dubbed healing [1] ) was later confirmed for other aluminum alloys such as commercially pure, [8] Al-Mg, [9,10] and Al-0.05 wt pct Sr. [11] Najafzadeh and Raiszadeh [8,9] concluded that, for the two layers of an oxide defect to bond with each other, two criteria must be met (1) complete consumption of O and N within the defect by the reaction with the surrounding melt, and (2) occurrence of a transformation involving the rearrangement of atoms at the internal surfaces of the oxide layers.…”

“…According to Aryafar et al, [7] the occurrence of such transformation is essential for the two oxide layers to bond with each other. Another criterion for a successful bonding is the absence of air or hydrogen in the trapped atmosphere of the defect.…”

“…Dissolved hydrogen in the melt diffuses into the trapped atmosphere of the oxide defect and keeps the oxide layers separate from each other, [4] and hence prevents them from bonding. Aryafar et al [7] observed that the bonding between the two layers of an oxide defect in Al-0.3 wt pct Mg occurred only after the H was diffused back to the ambient liquid Al (when the H content of the melt decreased due to equilibrating with the surrounding atmosphere). This reverse diffusion of H could take tens of minutes, [4] when, in the case of Al-Ca melts, it is too late for any bonding to occur, since the main part of the transformation in the oxide layers has occurred before this time.…”

“…More details of the experimental procedure can be found in another study by this research team. [7] B. Thermodynamic Study of Double Oxide Film Behavior Thermodynamics of the transformations that occurred in the Al-Ca-Al 2 O 3 system and the possible reactions between the dissolved Ca in the Al melt and the alumina layers on the surface of the Al bars were studied using Equilib-Web, a part of the Fact-web program. [14] These calculations determined the amount of oxides present in the Al-Ca-Al 2 O 3 system in the equilibrium state at 1000 K (727°C) and 1 atm for Ca concentrations of 0.01 and 0.05 wt pct in the melt.…”

Modification Behavior of Eutectic Si with Varying Heat Treatment Conditions in A356 Alloy with Al₂Ca

“…Al 합금 중에서도 Al-Si계 주조용 합금인 A356 (Al-7Si-0.4Mg) 합금은 가공성 및 유동성, 주조성이 우수한 합금으로 자동차, 국방, 항공기 등의 산업에 널리 이용되고 있다 [1][2][3].…”