Determination of Acceptable Quality Limit for Casting of A356 Aluminium Alloy: Supplier’s Quality Index (SQI)

Abstract

Aluminium and its alloys have been widely used in the automotive industry for some time and A356 is one of the most popular aluminium alloys today in the sector. It contains approximately 7 wt.% Si and 0.3 wt.% Mg. Due to the defects that may be present in the cast parts, expected mechanical properties may not be reached and this alloy may perform in service under its potential. In a low pressure die casting, several precautions have to be taken in order to produce high quality and defect-free castings. Temperature of casting and the schemical composition of the melt is recorded continuously. Die temperature, pressure levels and their durations are optimized; degassing and fluxing operations are performed. Yet, regardless of the precautions, there could still be rejected parts. It is becoming clear that a good quality raw material is one of the most underrated points of the industry and that the starting material has a great effect on the final product and it should be taken in to account more seriously. Therefore, regarding the first rule of Campbell's 10 Rules of Casting, in this study, the quality of the starting material of supply chains for a wheel manufacturer was investigated. Chemical compositions were compared, fluidity tests, mechanical tests and bifilm indexes of these various sources and ingots were measured and a final quality index was proposed to create a reference for the quantification of quality of supplier's ingots. This new index was compared with the rejection rates.

The Effects of Rotary Degassing Treatments on the Melt Quality of an Al–Si Casting Alloy

“…12 Bifilms have a central, unbounded interface; thus, these defects act like cracks in the microstructure of the solidified casting causing significantly lowered tensile strength, elongation and fatigue life. [13][14][15][16][17][18][19][20][21] Besides that, bifilms can easily open up and inflate into pores because of the hydrogen diffusion into their inner gas atmosphere and the local pressure drop in the mushy zone caused by the shrinkage during solidification. 7,8,[22][23][24][25][26] These negative effects highlight the importance of good liquid metal quality control via efficient melt treatments, which aim the reduction in inclusion (especially bifilm) and solute hydrogen content of the molten alloys.…”

Effects of Casting Conditions for Reduced Pressure Test on Melt Quality of Al-Si Alloy

“…As illustrated in Figure 1, Al melt quality can be evaluated by methods, including reduced pressure test, K-mold test, closed-loop recirculation, pressure filter technique, and thermal analysis; and a variety of studies have been under way to increase the accuracy of Al melt quality assessment [13][14][15][16][17][18][19][20]. For the reduced pressure test (RPT), while sampled Al melt is solidified in reduced pressure chamber at 1~10 KPa, bubble releases, cross-sectional porosity, and Density Index (DI) are half-quantitatively estimated to evaluate melt quality [13,14].…”

“…D. Dispinar and J. Campbel [15] proposed the Bifilm Index (BI), which measures the maximum length of bifilms on the sectioned RPT samples, as a quantitative indicator of the melt quality. Recently, E. Erzi et al [18] proposed Supplier's Qaulity Index (SQI) as a final quality index to create a reference for the quantification of quality of supplier's ingots. The SQI index was estimated by the measured values of yield stress, ultimate tensile strength, elongation at fracture, fluidity of the melt, and BI.…”

Numerical Simulation of Reoxidation Processes

“…The increasing demands on the aluminum alloys quality are related to the effort to eliminate as many casting defects as possible. One of the biggest problems in the production of castings from aluminum alloys is the reoxidation, which significantly affects the quality of liquid metal [1,2].…”

“…Liquid metal reacts with the surrounding atmosphere and oxide layer of Al2O3 is formed on its surface. Reoxidation is considered to be the secondary oxidation that occurs from the beginning of the casting process until the moment when the mold cavity is filled, as well as the tertiary oxidation that occurs during solidification [2,3]. The result of reoxidation processes are "bifilms", which are formed and entrainment into the bulk of liquid metal by turbulence.…”