How are aerospace castings tested for porosity and strength?

Aerospace castings are tested for porosity and strength with a risk-based combination of process control, qualified nondestructive testing, destructive material tests, and component-level structural or functional tests. Radiography or CT can investigate selected internal discontinuities; penetrant can find surface-breaking indications; tensile, hardness, microstructure, fatigue, fracture, and component tests address different material or structural questions. No single method proves that a casting is "porosity-free" or strong enough for flight. The design and quality authorities define critical zones, acceptance, sampling, qualified sources, and disposition.

Define the indication and its consequence

Gas pores, shrinkage, oxide films, inclusions, cold shuts, hot tears, cracks, laps, and machining breakout differ in shape, orientation, connectivity, and effect. Mark fatigue paths, fastener bosses, bearing seats, pressure walls, machined surfaces, thin load sections, thermal interfaces, and cosmetic-only zones. Acceptance should address type, size, location, orientation, clustering, and function rather than a global percentage.

Inspection does not improve the casting. Tool and process design, material/melt controls, fill and feeding, vents or vacuum where used, cooling, heat treatment, handling, and machining must prevent or control discontinuities. NDT verifies selected outcomes within its limitations.

Use radiography and CT for appropriate internal zones

Radiography creates a two-dimensional projection through the part. It can reveal density changes associated with some gas and shrinkage conditions, but sensitivity depends on thickness, orientation, overlap, geometry, exposure, image quality, technique, and interpretation. Plan views and coverage around critical zones; a generic full-part statement is not enough.

Computed tomography reconstructs volume data and can support development, process qualification, dimensional investigation, or selected production inspection. Resolution depends on part size, material path, equipment, setup, reconstruction, artifacts, and threshold method. Report detectable size and uncertainty for the actual part. CT volume percentages should not be converted directly into fatigue acceptance without a structural basis.

Use surface NDT after the relevant processing

Liquid penetrant can indicate discontinuities open to a clean surface. Surface condition, coating, machining, blasting, cleaning, penetrant family, dwell, removal, developer, lighting, personnel, and acceptance affect results. Inspect at the process stage specified by the plan because machining or heat treatment can reveal indications that were not accessible earlier.

Other authorized surface or volumetric methods may apply to specific materials, geometries, and programs. Each requires a written practice, qualified procedure, qualified personnel, calibrated equipment, reference standards where applicable, and documented evaluation. Method names on a capability list do not establish approval.

Verify material condition with destructive tests

Chemistry, tensile, hardness, conductivity, microstructure, density, corrosion, or other tests can verify specified aspects of material and heat treatment. Define whether specimens are separately cast, attached, machined from a casting, or cut from designated zones. Location, orientation, section, surface, heat-treatment load, and lot relationship determine what the result represents.

A356 or another alloy name does not supply a universal strength value. Compare results only to the invoked material/process specification and approved design basis. Hardness can help monitor heat treatment but is not a substitute for tensile, fatigue, fracture, or component performance unless a validated correlation exists.

Test the component for the real load and environment

Static proof or ultimate, fatigue spectrum, vibration, shock, pressure, leak, thermal cycle, environmental, modal, electrical, and functional tests may be needed according to part classification. Use production-intent alloy, route, tool/cavity, heat treatment, machining, finish, inserts, fasteners, and assembly. Record configuration, load, environment, instrumentation, acceptance, anomalies, and post-test inspection.

Component tests support the tested configuration and plan; they do not erase production variation. Structural substantiation may also require analysis, material allowables, damage-tolerance or safe-life methods, and platform-level tests. The design authority determines the evidence set.

Match each question to the method

Control records and disposition

Link results to material heat, melt/lot, tool and cavity, heat-treatment load, machining state, special-process batch, NDT technique, equipment, personnel, acceptance revision, rework, and part serial or lot. Retain images, scans, raw or processed data, reports, test pieces, and records as contractually required. Protect digital data from unauthorized change.

Indications need authorized evaluation. Do not average a critical indication into a whole-part porosity value or accept it because a tensile coupon passed. Nonconformance, review authority, repair, reinspection, use-as-is, containment, and change must follow the approved system.

Testing equipment is only one part of this chain. Qualified techniques, people, acceptance, traceability, and design relevance are what turn inspection data into an aerospace release decision.