Metal-matrix-composites, MMCs, with ceramic reinforcement have received extensive studies during the past decades because of their improved mechanical properties. In the case of light alloys, MMCs present an interesting specific strength-temperature ratio up to 400 ◦C for Al-MMCs, 600 ◦C for Ti-MMCs and 900 ◦C for Ni-MMCs [1]. Among these composites, Al-MMCs are the lightest ones. Many investigations have been performed on aluminum-based composites reinforced by SiC or Al2O3 particles [1–3]. Nevertheless, due to the difference in thermal expansion coefficients between the reinforcement and the matrix, and also to interfacial reactions occurring during the process, some problems remain when parts have to be welded. Compared to Al-SiCp composites, few results have been published on the Al-AlNp systems, although some advantages are expected due to the non-reactivity of AlN with aluminum [4–9]. The scope of this paper is to present the effects of AlN additions and heat treatments on the mechanical behavior of three different Al-AlNp composites [9]. Aluminum-matrix composites containing ∼45 vol% AlN particles were fabricated by an original melt infiltration process of aluminum alloys into an AlN perform under a pressure up to 130 MPa. This process has already been described [10]. Three types of aluminum alloys (2024, 6060 and 5754) and two types of AlN powders were used: AlNESK from Elektroschmelzwerk (Kempten, Germany) with a mean particle size of 20–30 μm and AlNStark from H. C. Starck (Goslar, Germany), (6–7 μm). Table I summarizes the characteristics of the composites. They will be denoted AlCu4Mg1-45%AlN, AlMgSi0.5-42%AlN and AlMg3-48%AlN in the following. Two composites possess an age-hardenable matrix. They were subjected to T4 (AlCu4Mgl or 2024) and T6 (AlMgSi0.5 or 6060) heat treatments. Long term annealings (10 and 20 days at 300 and 550 ◦C) were carried out to favor possible reactions between the Al matrices and AlN. Using a diamond saw, specimens were cut from the composite parts to obtain 4 × 4 × 8 mm3 samples for compression tests. They were machined up with parallel faces with accuracy better than 1 μm. Compression tests were performed with an Instron 1380 machine (Bucks, England), in air. An example of an AlMgSi0.5– 42%AlN sample before and after a compression test is shown in Fig. 1. The load cell was 30 kN and the loading