Conditions for blister formation during thermal cycles of Al–Si–Cu–Fe alloys for high pressure die-casting

OksanaOzhoga-MaslovskajaElisabettaGariboldiJannis NicolasLemkeShow moreAdd to MendeleyShareCite

https://doi.org/10.1016/j.matdes.2015.12.003Get rights and content

Highlights

•

Critical conditions for blister formation of Al–9Si–3Cu–Fe alloy are identified via a FE model.•

Blister formation is modeled for wide range of temperatures, pore pressure, shape, location, and size.•

Strain field shows blister formation related to strain localization, depending of pore geometry.•

Lamina-shaped discontinuities of cast part are most critical for blister formation.

Abstract

The mechanism of blister formation during thermal cycle in a High Pressure Die Cast Al–9Si–3Cu–Fe alloy (EN 46000) was investigated by means of FEM simulation of a pressurized subsurface defect, considering the high-temperature elastoplastic behavior experimentally derived. The effect of parameters related to initial defect geometry, location and maximum temperature was analyzed. Blister formation was considered to occur as the maximum surface displacement after a thermal cycle exceeded 0.005 mm. It was shown that, for a given reference gas pressure, pore volume and depth, as well as temperature, blisters were developed from pores below a critical aspect ratio, as a result of high plastic strain accumulation in localized regions laying between the pore and the outer surface (ligament). Similarly, critical ligament thickness was identified and correlated to temperature and reference gas pressure. The development of blisters at temperatures lower than 400 °C from pores with reference pressure 90 MPa was predicted for a wide range of aspect ratios and ligament thickness. The possible occurrence of blisters in conventional HPDC components during heat treatment cycles at 350 °C was modeled for different pore pressures in the case of surface-near defects, mainly from lamina-shaped pores and was experimentally confirmed.

고압 다이 캐스트 Al-9Si-3Cu-Fe 합금(EN 46000)에서 열 사이클 중 블리스터 형성 메커니즘은 실험적으로 도출된 고온 탄소성 거동을 고려하여 가압된 표면 결함의 FEM 시뮬레이션을 통해 조사되었습니다. 초기 결함 형상, 위치 및 최대 온도와 관련된 매개변수의 영향을 분석했습니다.

블리스터 형성은 열 사이클 후 최대 표면 변위가 0.005mm를 초과할 때 발생하는 것으로 간주되었습니다. 주어진 기준 가스 압력, 기공 부피 및 깊이, 온도에 대해 기공과 기공 사이에 있는 국부적 영역에서 높은 소성 변형 축적의 결과로 임계 종횡비 미만의 기공에서 기포가 발생하는 것으로 나타났습니다.

외부 표면 (인대). 유사하게 임계 인대 두께가 식별되었고 온도 및 기준 가스 압력과 상관관계가 있었습니다. 기준 압력이 90MPa인 기공에서 400°C 미만의 온도에서 기포가 발생하는 것은 광범위한 종횡비 및 인대 두께에 대해 예측되었습니다.

350°C에서 열처리 주기 동안 기존 HPDC 구성 요소에서 기포가 발생할 가능성은 주로 박판 모양의 기공에서 발생하는 표면 근처 결함의 경우 다양한 기공 압력에 대해 모델링되었으며 실험적으로 확인되었습니다.

Graphical abstract

Fig. 3. Axisymmetric FE model of the solid, containing an elliptic pore with applied boundary conditions and inner pore pressure.
Fig. 3. Axisymmetric FE model of the solid, containing an elliptic pore with applied boundary conditions and inner pore pressure.
Fig. 4. Localized plastic strains generated by the pore with C/A = 0.53, 7.5°10−6 mm3 pore volume, H = 0.0245 mm and reference inner pressure ps of 30 MPa at different temperatures during heating: a) 25 °C; b) 420 °C; c) 440 °C and d) at room temperature T0 = 25 °C after cooling. Note that the color scale for plastic strains, plotted on the deformed shape limited by the value of maximum principal plastic strains equal to 0.2 mm/mm.
Fig. 4. Localized plastic strains generated by the pore with C/A = 0.53, 7.5°10−6 mm3 pore volume, H = 0.0245 mm and reference inner pressure ps of 30 MPa at different temperatures during heating: a) 25 °C; b) 420 °C; c) 440 °C and d) at room temperature T0 = 25 °C after cooling. Note that the color scale for plastic strains, plotted on the deformed shape limited by the value of maximum principal plastic strains equal to 0.2 mm/mm.
Fig. 5. Localized plastic strains generated by the pore with C/A = 0.06, pore volume of 7.5°10−6 mm3 , H = 0.0245 mm and reference inner pressure ps of 30 MPa at different temperatures during heating: a) 25 °C; b) 360 °C; c) 390 °C; d) and at room temperature (T0 = 25 °C) after cooling. Also in these figures the plastic strains are plotted on the deformed shape and the notes about the color scales for Fig. 4 are to be considered.
Fig. 5. Localized plastic strains generated by the pore with C/A = 0.06, pore volume of 7.5°10−6 mm3 , H = 0.0245 mm and reference inner pressure ps of 30 MPa at different temperatures during heating: a) 25 °C; b) 360 °C; c) 390 °C; d) and at room temperature (T0 = 25 °C) after cooling. Also in these figures the plastic strains are plotted on the deformed shape and the notes about the color scales for Fig. 4 are to be considered.

Keywords

Blister

High pressure die casting

Thermal cycle

Al–9Si–3Cu–Fe alloy (EN 46000)

High temperature behavior

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